Amino acid derivatives

ABSTRACT

The present invention relates to a method of treating pain using a compound of formula 
                         
wherein R 1 , R 2 , R 3  and R 4  are as defined herein. The invention also relates to certain novel derivatives of formula (I).

This application is a U.S. non-provisional application, which claims thebenefits of priority to U.S. Provisional Application No. 60/676,025,file Apr. 28, 2005.

This invention relates to α-amino acid derivatives derivatives. Moreparticularly, this invention relates to α,α-disubstituted-α-amino acidderivatives and to processes for the preparation of, intermediates usedin the preparation of, compositions containing and the uses of suchderivatives.

The compounds of the present invention are alpha-2-delta (α2δ) receptorligands (also known as alpha-2-delta ligands) and as such are useful inthe treatment of a number of different diseases. An alpha-2-deltareceptor ligand is a molecule which binds to any sub-type of the humancalcium channel alpha-2-delta subunit. The calcium channel alpha-2-deltasubunit comprises a number of sub-types which have been described in theliterature (e.g. type 1, J. Biol. Chem., 1996, 271(10), 5768-76; types 2and 3, J. Membr. Biol., 2001, 184(1), 35-43 and Mol. Pharmacol., 2001,59(5), 1243-1248, 2001; and type 4, Mol. Pharmacol., 2002, 62(3),485-496). Alpha-2-delta receptor ligands are also sometimes known asGABA analogues.

Among known alpha-2-delta ligands are marketed drugs such as gabapentin(sold under the trade mark Neurontin) and pregabalin (sold under thetrade mark Lyrica). Gabapentin is an anti-convulsant which is marketedfor the treatment of epilepsy. Pregabalin is marketed for the treatmentof neuropathic pain.

There is always a need to provide new drugs, which potentially haveimproved properties (e.g. greater potency, greater selectivity, betterabsorption from the gastrointestinal tract, greater metabolic stabilityand more favourable pharmacokinetic properties). Other potentialadvantages include greater or lesser penetration of the blood brainbarrier, according to the disease targeted, lower toxicity and adecreased incidence of side-effects.

The invention therefore provides, as embodiment A, the use of a compoundof formula (I):

or a pharmaceutically acceptable salt or solvate thereof, wherein

-   R¹ is C₁-C₆ alkyl, said C₁-C₆ alkyl being optionally substituted by    one or more halo, —R⁵, —OR⁵ or —SR⁵ groups;-   R² is methyl, optionally substituted by one or more fluoro groups;-   R³ is H, (C₁-C₆ alkyl), aryl, indanyl or (C₁-C₆    alkyl)oxycarbonyloxy(C₁-C₆ alkyl);-   R⁴ is H, (C₁-C₆ alkyl)C(O)—, arylC(O)—, or a natural α-amino acid    residue linked through its carboxyl group to form an amide;-   R⁵ is C₁-C₆ alkyl, C₁-C₆ haloalkyl, C₃-C₈ cycloalkyl or aryl;-   aryl is phenyl or naphthyl, each optionally substituted by one or    more substituents selected from halo, —NR⁶R⁶, C₁-C₆ alkyl, C₃-C₈    cycloalkyl, C₁-C₆ alkoxy and cyano; and-   R⁶ is H, C₁-C₆ alkyl or C₃-C₈ cycloalkyl;    for the manufacture of a medicament for the treatment of pain.

The invention further provides, as embodiment B, a compound of formula(II):

or a pharmaceutically acceptable salt or solvate thereof, wherein

-   R⁷ is:    -   (a) branched C₆-C₁₀ alkyl, other than 4-methylpent-1-yl and        1-methylpent-1-yl;    -   (b) C₂-C₆ alkyl substituted by one or more flouro groups, other        than 1-fluoroeth-1-yl, heptafluoropropyl,        2,2-ditrifluoromethyleth-1-yl, pentafluoroethyl,        2-fluoroeth-1-yl, 2-fluoropent-1-yl and        2-fluoro-3-methylbut-1-yl;    -   (c) C₁-C₆ alkyl substituted by one C₃-C₈ cycloalkyl group, other        than cyclohexylmethyl;    -   (d) ethyl substituted by one aryl group, other than where aryl        is phenyl or phenyl substituted by an —NH₂, iodo or methoxy        group (regardless of other substitution);    -   (e) C₃-C₄ alkyl substituted by aryl, other than where aryl is        phenyl, 3,4-dihydroxyphenyl or 3,4-dimethoxyphenyl;    -   (f) C₅-C₆ alkyl substituted by aryl;    -   (g) C₁-C₂ alkyl substituted by C₅-C₆ alkoxy;    -   (h) C₃-C₆ alkyl substituted by C₁-C₆ alkoxy;    -   (i) C₁-C₆ alkyl substituted by C₃-C₈ cycloalkyloxy;    -   (j) C₁-C₆ alkyl substituted by aryloxy, other than        (2-methoxyphenyl)oxymethyl, (4-methoxyphenyl)oxymethyl,        (4-chlorophenyl)oxymethyl, (2,6-dimethylphenyl)oxymethyl,        (2-methoxy-5-chlorophenyl)oxymethyl,        (2-methoxy-5-fluorophenyl)oxymethyl and        (2-methoxy-4-chlorophenyl)oxymethyl;    -   (k) methyl substituted by hexylthio or C₄-C₆ alkyl substituted        by C₁-C₆ alkylthio;    -   (l) C₁-C₆ alkyl substituted by C₃-C₈ cycloalkylthio, other than        cyclohexylthiomethyl; or    -   (m) C₁-C₆ alkyl substituted by arylthio, other than        phenylthiomethyl, (4-chlorophenyl)thiomethyl,        (4-fluorophenyl)thiomethyl, 2-(phenylthio)ethyl,        (4-chlorophenyl)thioethyl, (4-methoxyphenyl)thiomethyl and        (4-methoxyphenyl)thioethyl;-   R⁸ is methyl, optionally substituted with one or more fluoro groups;-   aryl is phenyl or naphthyl, each optionally substituted by one or    more substituents selected from halo, —NR⁹R⁹, C₁-C₆ alkyl, C₃-C₈    cycloalkyl, C₁-C₆ alkoxy and cyano; and-   R⁹ is H, C₁-C₆ alkyl or C₃-C₈ cycloalkyl.

In the above definitions, halo means fluoro, chloro or bromo and ispreferably fluoro or chloro. Alkyl and alkoxy groups containing therequisite number of carbon atoms can, unless otherwise specified, beunbranched or branched chain. Examples of alkyl include methyl, ethyl,n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl and t-butyl. Examples ofalkoxy include methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy,i-butoxy, sec-butoxy and t-butoxy. Examples of cycloalkyl includecyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and cycloheptyl.

In embodiment Aa, the invention provides the use of a compound offormula (I), or a pharmaceutically acceptable salt or solvate thereof,wherein R³ and R⁴ are both H and R¹ and R² are as defined above inembodiment A, for the manufacture of a medicament for the treatment ofpain.

In embodiment Ab, the invention provides the use of a compound offormula (I), or a pharmaceutically acceptable salt or solvate thereof,wherein R³ and R⁴ are as defined above in embodiment A or embodiment Aa,R¹ is as defined in embodiment A and R² is methyl, for the manufactureof a medicament for the treatment of pain.

In embodiment Ac, the invention provides the use of a compound offormula (I), or a pharmaceutically acceptable salt or solvate thereof,wherein R³ and R⁴ are as defined above in embodiment A or embodiment Aa,R² is as defined above in embodiment A or embodiment Ab and R¹ is:

-   -   (a) C₁-C₂ alkyl, said C₁-C₂ alkyl being optionally substituted        by one or more halo, —R⁵, —OR⁵ or —SR⁵ groups, R⁵ being as        defined in embodiment A; or    -   (b) unsubstituted C₅-C₇ alkyl or C₁-C₂ alkyl substituted with        one group selected from C₃-C₈ cycloalkyl, aryl or aryloxy, aryl        being as defined in embodiment A;    -   (c) branched, unsubstituted C₅-C₇ alkyl or C₁-C₂ alkyl        substituted with one group selected from C₃-C₈ cycloalkyl, aryl        or aryloxy, aryl being as defined in embodiment A;    -   (d) ethylbutyl, dimethylbutyl, ethylpentyl, methylpentyl,        methylbutyl, cyclopentylmethyl, cyclobutylmethyl,        cyclopropylethyl, phenyloxyethyl or chlorophenylmethyl; or    -   (e) 2-ethyl-but-1-yl, 3,3-dimethylbut-1-yl, 3-ethylpent-1-yl,        3-methylpent-1-yl, 2-methylbut-1-yl, 3-methylbut-1-yl,        4-methylpent-1-yl, cyclopentylmethyl, cyclobutylmethyl,        2-cyclopropyleth-1-yl, 2-(phenyloxy)eth-1-yl or        (3-chlorophenyl)methyl;        for the manufacture of a medicament for the treatment of pain.

In embodiment Ba, the invention provides a compound of formula (II), ora pharmaceutically acceptable salt or solvate thereof, wherein R⁷ is asdefined above in embodiment B and R⁸ is methyl.

In embodiment Bb, the invention provides a compound of formula (II), ora pharmaceutically acceptable salt or solvate thereof, wherein R⁸ is asdefined above in embodiment B or embodiment Ba and R⁷ is:

-   -   (a) branched C₆-C₇ alkyl, other than 4-methylpent-1-yl and        1-methylpent-1-yl; C₁-C₂ alkyl substituted by one C₃-C₈        cycloalkyl group, other than cyclohexylmethyl; C₁-C₂ alkyl        substituted by aryloxy, other than (2-methoxyphenyl)oxymethyl,        (4-methoxyphenyl)oxymethyl, (4-chlorophenyl)oxymethyl,        (2,6-dimethylphenyl)oxymethyl,        (2-methoxy-5-chlorophenyl)oxymethyl,        (2-methoxy-5-fluorophenyl)oxymethyl and        (2-methoxy-4-chlorophenyl)oxymethyl; 2-methylbutyl; or        chlorophenylmethyl; or    -   (b) 2-ethyl-but-1-yl, 3,3-dimethylbut-1-yl, 3-ethylpent-1-yl,        3-methylpent-1-yl, 2-methylbut-1-yl, 4-methylpent-1-yl,        cyclopentylmethyl, cyclobutylmethyl, 2-cyclopropyleth-1-yl,        2-(phenyloxy)eth-1-yl or (3-chlorophenyl)methyl.

Specific preferred compounds according to the invention are those listedin the Examples section below and the pharmaceutically acceptable saltsand solvates thereof.

Further examples of compounds for use in the invention are:

-   3-chloro-alpha-methyl-L-phenylalanine;-   4-phenoxy-L-isovaline;-   2,5-dimethyl-L-norleucine; and-   (2S)-2-amino-4-cyclopropyl-2-methylbutanoic acid;    and the pharmaceutically acceptable salts and solvates thereof.

It should be noted that compounds of formula (II) are all also compoundsof formula (I), being those compounds of formula (I) which are novel perse. Consequently, all references to compounds of formula (I) belowshould be understood to refer to compounds of formula (II) as well.

Pharmaceutically acceptable salts of compounds of formula (I) includethe acid addition and base salts thereof.

Suitable acid addition salts are formed from acids which form non-toxicsalts. Examples include the acetate, aspartate, benzoate, besylate,bicarbonate/carbonate, bisulphate/sulphate, borate, camsylate, citrate,edisylate, esylate, formate, fumarate, gluceptate, gluconate,glucuronate, hexafluorophosphate, hibenzate, hydrochloride/chloride,hydrobromide/bromide, hydroiodide/iodide, isethionate, lactate, malate,maleate, malonate, mesylate, methylsulphate, naphthylate, 2-napsylate,nicotinate, nitrate, orotate, oxalate, palmitate, pamoate,phosphate/hydrogen phosphate/dihydrogen phosphate, saccharate, stearate,succinate, tartrate, tosylate and trifluoroacetate salts.

Suitable base salts are formed from bases which form non-toxic salts.Examples include the aluminium, arginine, benzathine, calcium, choline,diethylamine, diolamine, glycine, lysine, magnesium, meglumine, olamine,potassium, sodium, tromethamine and zinc salts.

Hemisalts of acids and bases may also be formed, for example,hemisulphate and hemicalcium salts.

For a review on suitable salts, see Handbook of Pharmaceutical Salts:Properties, Selection, and Use by Stahl and Wermuth (Wiley-VCH,Weinheim, Germany, 2002).

Pharmaceutically acceptable salts of a compound of formula (I) may beprepared by one or more of three methods:

-   -   (i) by reacting the compound of formula (I) with the desired        acid or base;    -   (ii) by removing an acid- or base-labile protecting group from a        suitable precursor of the compound of formula (I) or by        ring-opening a suitable cyclic precursor, for example, a lactone        or lactam, using the desired acid or base; or    -   (iii) by converting one salt of the compound of formula (I) to        another by reaction with an appropriate acid or base or by means        of a suitable ion exchange column.

All three reactions are typically carried out in solution. The resultingsalt may precipitate out and be collected by filtration or may berecovered by evaporation of the solvent. The degree of ionisation in theresulting salt may vary from completely ionised to almost non-ionised.

A compound of formula (I) in which R³ and R⁴ are H has a basic aminogroup and an acidic carboxy group and will exist, at physiological pH,as a zwitterion.

A compound of formula (I) may exist in both unsolvated and solvatedforms. The term ‘solvate’ is used herein to describe a molecular complexcomprising the compound of formula (I) and a stoichiometric amount ofone or more pharmaceutically acceptable solvent molecules, for example,ethanol. The term ‘hydrate’ is employed when said solvent is water.

Included within the scope of the invention are complexes such asclathrates, drug-host inclusion complexes wherein, in contrast to theaforementioned solvates, the drug and host are present in stoichiometricor non-stoichiometric amounts. Also included are complexes of the drugcontaining two or more organic and/or inorganic components which may bein stoichiometric or non-stoichiometric amounts. The resulting complexesmay be ionised, partially ionised, or non-ionised. For a review of suchcomplexes, see J. Pharm. Sci., 64 (8), 1269-1288, by Haleblian (August1975).

Hereinafter, all references to a compound of formula (I) includereferences to salts, solvates and complexes thereof and to solvates andcomplexes of salts thereof.

A compound of formula (I), as hereinbefore defined, may exist in one ormore crystalline (polymorphic) or isomeric forms (including optical,geometric and tautomeric isomers), in an isotopically labelled form oras a prodrug. All such crystalline/isomeric forms and prodrugs arewithin the scope of the present invention and are further describedbelow. All references to a compound of formula (I) should be interpretedaccordingly.

Included within the scope of the invention are compounds of the formula(I) wherein R³ and/or R⁴ is a group which is converted to H followingadministration of the compound to a mammal (preferably a human). Suchcompounds are known as prodrugs. Thus, these derivatives, which may havelittle or no pharmacological activity themselves can, when administeredinto or onto the body, be converted into compounds of formula (I)wherein R³ and R⁴ are both H, such compounds having the desired activityas alpha-2-delta ligands. Such prodrugs can be converted, for example,by hydrolytic cleavage.

Typically, R³ is an alkyl group, preferably a C₁-C₆ alkyl group.Specific examples of suitable alkyl groups are ethyl, isopropyl andn-butyl. Alternatively, R³ can be an aryl group (wherein aryl is asdefined above), such as phenyl, or an indanyl group. In other suitableembodiments R³ can be an alkyloxycarbonyloxyalkyl group, such as—CH₂OC(O)O^(t)Bu, —CH(CH₃)OC(O)OEt or —CH(CH₃)OC(O)O^(i)Pr (see Journalof Pharmacology and Experimental Therapeutics, 311, 1, 324-335) or acyclic carbonate linked via a methylene group.

Typically, R⁴ is an amide-forming group such as —CO(C₁-C₆ alkyl) or—CO(aryl) (wherein aryl is as defined above). Specific examples aremethylcarbonyl, isopropylcarbonyl and phenylcarbonyl. Alternatively, R⁴may be an α-amino acid residue joined through its carboxyl group to forman amide. The naturally occurring amino acids, particularly glycine,alanine and valine are preferred.

Whether or not a particular compound will act as a prodrug and behydrolytically cleaved to the active compound in vivo may be accuratelyassessed using a number of in vitro tests and in vivo animal models.Prodrug hydrolysis can be characterised in vitro using a range of tissuefractions including simple homogenates and microsomes: see, for example,Journal of Pharmacology and Experimental Therapeutics, 294, 2, 580-587;Life Sci., 62, 14, 1231-124; International Journal of Pharmaceutics,166, 1, 45-53; and Toxicol. Lett., 82-83, 439-445. Rat liver microsomehomogenates are particularly useful in this regard. In vivo assays canalso be used to investigate prodrug properties. Intravenous and oralpharmacokinetics with both the active principle and the prodrug providesinformation about the relative bioavailability of the prodrug, theability of the body to hydrolyse the prodrug and the rate of hydrolysisto the active species (see Antimicrob. Agents. Chemother. 42, 3,647-653). A proposed screening strategy for assaying prodrugs has beengiven in a recent review (Current Drug Metabolism, 2003, vol 4, no. 6, p483).

Further information on the use of prodrugs may be found in Pro-drugs asNovel Delivery Systems, Vol. 14, ACS Symposium Series (T. Higuchi and W.Stella) and Bioreversible Carriers in Drug Design, Pergamon Press, 1987(ed. E. B. Roche, American Pharmaceutical Association).

Prodrugs of compounds of the formula (I) other than those involving R³and R⁴ groups are also within the scope of the invention and can, forexample, be produced by replacing appropriate functionalities present inthe compounds of formula (I) with certain moieties known to thoseskilled in the art as ‘pro-moieties’ as described, for example, inDesign of Prodrugs by H. Bundgaard (Elsevier, 1985).

Some examples of other prodrugs in accordance with the inventioninclude, where the compound of formula (I) contains a primary orsecondary amino functionality (—NH₂ or —NHR where R≠H), an amidethereof, for example, a compound wherein, as the case may be, one orboth hydrogens of the amino functionality of the compound of formula (I)is/are replaced by (C₁-C₁₀)alkanoyl.

Moreover, certain compounds of formula (I) may themselves act asprodrugs of other compounds of formula (I).

Also included within the scope of the invention are metabolites ofcompounds of formula (I), that is, compounds formed in vivo uponadministration of the drug. Some examples of metabolites in accordancewith the invention include

-   (i) where the compound of formula (I) contains a methyl group, an    hydroxymethyl derivative thereof (—CH₃→—CH₂OH):-   (ii) where the compound of formula (I) contains an alkoxy group, an    hydroxy derivative thereof (—OR→—OH);-   (iii) where the compound of formula (I) contains a tertiary amino    group, a secondary amino derivative thereof (—NR¹R²→—NHR¹ or —NHR²);-   (iv) where the compound of formula (I) contains a secondary amino    group, a primary derivative thereof (—NHR¹→—NH₂);-   (v) where the compound of formula (I) contains a phenyl moiety, a    phenol derivative thereof (-Ph→-PhOH); and

Compounds of formula (I) containing a further asymmetric carbon atom canexist as diastereomers. Where structural isomers are interconvertiblevia a low energy barrier, tautomeric isomerism (‘tautomerism’) canoccur. This can take the form of proton tautomerism or so-called valencetautomerism. It follows that a single compound may exhibit more than onetype of isomerism.

Included within the scope of the present invention are alldiastereomers, and tautomeric forms of the compounds of formula (I),including compounds exhibiting more than one type of isomerism, andmixtures of one or more thereof. Also included are acid addition or basesalts wherein the counterion is optically active, for example, d-lactateor l-lysine, or racemic, for example, dl/tartrate or dl-arginine.

Diastereomers may be separated by conventional techniques well known tothose skilled in the art, for example, chromatography and fractionalcrystallisation.

Compounds of the formula (I) are α-amino acids with a definedstereochemistry at the α-carbon atom. Conventional techniques for thepreparation/isolation of individual enantiomers include chiral synthesisfrom a suitable optically pure precursor or resolution of the racemate(or the racemate of a salt or derivative) using, for example, chiralhigh pressure liquid chromatography (HPLC).

Alternatively, the racemate (or a racemic precursor) may be reacted witha suitable optically active compound. The resulting diastereomericmixture may be separated by chromatography and/or fractionalcrystallization and one or both of the diastereoisomers converted to thecorresponding pure enantiomer(s) by means well known to a skilledperson.

Enantiomerically-enriched compounds may also be obtained usingchromatography, typically HPLC, on an asymmetric resin with a mobilephase consisting of a hydrocarbon, typically heptane or hexane,containing from 0 to 50% by volume of isopropanol, typically from 2% to20%, and from 0 to 5% by volume of an alkylamine, typically 0.1%diethylamine. Concentration of the eluate affords the enriched mixture.

Stereoisomeric conglomerates may be separated by conventional techniquesknown to those skilled in the art—see, for example, Stereochemistry ofOrganic Compounds by E. L. Eliel and S. H. Wilen (Wiley, New York,1994).

Examples of isotopes suitable for inclusion in the compounds of theinvention include isotopes of hydrogen, such as ²H and ³H, carbon, suchas ¹¹C, ¹³C and ¹⁴C, chlorine, such as ³⁶Cl, fluorine, such as ¹⁸F,iodine, such as ¹²³I and ¹²⁵I, nitrogen, such as ¹³N and ¹⁵N, oxygen,such as ¹⁵O, ¹⁷O and ¹⁸O, phosphorus, such as ³²P, and sulphur, such as³⁵S.

Certain isotopically-labelled compounds of formula (I), for example,those incorporating a radioactive isotope, are useful in drug and/orsubstrate tissue distribution studies. The radioactive isotopes tritium,i.e. ³H, and carbon-14, i.e. ¹⁴C, are particularly useful for thispurpose in view of their ease of incorporation and ready means ofdetection.

Substitution with heavier isotopes such as deuterium, i.e. ²H, mayafford certain therapeutic advantages resulting from greater metabolicstability, for example, increased in vivo half-life or reduced dosagerequirements, and hence may be preferred in some circumstances.

Substitution with positron emitting isotopes, such as ¹¹C, ¹⁸F, ¹⁵O and¹³N, can be useful in Positron Emission Topography (PET) studies forexamining substrate receptor occupancy.

Isotopically-labeled compounds of formula (I) can generally be preparedby conventional techniques known to those skilled in the art or byprocesses analogous to those described in the accompanying Examples andPreparations using an appropriate isotopically-labeled reagent in placeof the non-labeled reagent previously employed.

Pharmaceutically acceptable solvates in accordance with the inventioninclude those wherein the solvent of crystallization may be isotopicallysubstituted, e.g. D₂O, d₆-acetone, d₆-DMSO.

The compounds of formula (I), being alpha-2-delta receptor ligands, arepotentially useful in the treatment of a wide range of disorders. Thetreatment of pain, particularly neuropathic pain, is a preferred use.

Physiological pain is an important protective mechanism designed to warnof danger from potentially injurious stimuli from the externalenvironment. The system operates through a specific set of primarysensory neurones and is activated by noxious stimuli via peripheraltransducing mechanisms (see Millan, 1999, Prog. Neurobiol., 57, 1-164for a review). These sensory fibres are known as nociceptors and arecharacteristically small diameter axons with slow conduction velocities.Nociceptors encode the intensity, duration and quality of noxiousstimulus and by virtue of their topographically organised projection tothe spinal cord, the location of the stimulus. The nociceptors are foundon nociceptive nerve fibres of which there are two main types, A-deltafibres (myelinated) and C fibres (non-myelinated). The activitygenerated by nociceptor input is transferred, after complex processingin the dorsal horn, either directly, or via brain stem relay nuclei, tothe ventrobasal thalamus and then on to the cortex, where the sensationof pain is generated.

Pain may generally be classified as acute or chronic. Acute pain beginssuddenly and is short-lived (usually in twelve weeks or less). It isusually associated with a specific cause such as a specific injury andis often sharp and severe. It is the kind of pain that can occur afterspecific injuries resulting from surgery, dental work, a strain or asprain. Acute pain does not generally result in any persistentpsychological response. In contrast, chronic pain is long-term pain,typically persisting for more than three months and leading tosignificant psychological and emotional problems. Common examples ofchronic pain are neuropathic pain (e.g. painful diabetic neuropathy,postherpetic neuralgia), carpal tunnel syndrome, back pain, headache,cancer pain, arthritic pain and chronic post-surgical pain.

When a substantial injury occurs to body tissue, via disease or trauma,the characteristics of nociceptor activation are altered and there issensitisation in the periphery, locally around the injury and centrallywhere the nociceptors terminate. These effects lead to a hightenedsensation of pain. In acute pain these mechanisms can be useful, inpromoting protective behaviours which may better enable repair processesto take place. The normal expectation would be that sensitivity returnsto normal once the injury has healed. However, in many chronic painstates, the hypersensitivity far outlasts the healing process and isoften due to nervous system injury. This injury often leads toabnormalities in sensory nerve fibres associated with maladaptation andaberrant activity (Woolf & Salter, 2000, Science, 288, 1765-1768).

Clinical pain is present when discomfort and abnormal sensitivityfeature among the patient's symptoms. Patients tend to be quiteheterogeneous and may present with various pain symptoms. Such symptomsinclude: 1) spontaneous pain which may be dull, burning, or stabbing; 2)exaggerated pain responses to noxious stimuli (hyperalgesia); and 3)pain produced by normally innocuous stimuli (allodynia—Meyer et al.,1994, Textbook of Pain, 13-44). Although patients suffering from variousforms of acute and chronic pain may have similar symptoms, theunderlying mechanisms may be different and may, therefore, requiredifferent treatment strategies. Pain can also therefore be divided intoa number of different subtypes according to differing pathophysiology,including nociceptive, inflammatory and neuropathic pain.

Nociceptive pain is induced by tissue injury or by intense stimuli withthe potential to cause injury. Pain afferents are activated bytransduction of stimuli by nociceptors at the site of injury andactivate neurons in the spinal cord at the level of their termination.This is then relayed up the spinal tracts to the brain where pain isperceived (Meyer et al., 1994, Textbook of Pain, 13-44). The activationof nociceptors activates two types of afferent nerve fibres. MyelinatedA-delta fibres transmit rapidly and are responsible for sharp andstabbing pain sensations, whilst unmyelinated C fibres transmit at aslower rate and convey a dull or aching pain. Moderate to severe acutenociceptive pain is a prominent feature of pain from central nervoussystem trauma, strains/sprains, burns, myocardial infarction and acutepancreatitis, post-operative pain (pain following any type of surgicalprocedure), posttraumatic pain, renal colic, cancer pain and back pain.Cancer pain may be chronic pain such as tumour related pain (e.g. bonepain, headache, facial pain or visceral pain) or pain associated withcancer therapy (e.g. postchemotherapy syndrome, chronic postsurgicalpain syndrome or post radiation syndrome). Cancer pain may also occur inresponse to chemotherapy, immunotherapy, hormonal therapy orradiotherapy. Back pain may be due to herniated or rupturedintervertabral discs or abnormalities of the lumber facet joints,sacroiliac joints, paraspinal muscles or the posterior longitudinalligament. Back pain may resolve naturally but in some patients, where itlasts over 12 weeks, it becomes a chronic condition which can beparticularly debilitating.

Neuropathic pain is currently defined as pain initiated or caused by aprimary lesion or dysfunction in the nervous system. Nerve damage can becaused by trauma and disease and thus the term ‘neuropathic pain’encompasses many disorders with diverse aetiologies. These include, butare not limited to, peripheral neuropathy, diabetic neuropathy, postherpetic neuralgia, trigeminal neuralgia, back pain, cancer neuropathy,HIV neuropathy, phantom limb pain, carpal tunnel syndrome, centralpost-stroke pain and pain associated with chronic alcoholism,hypothyroidism, uremia, multiple sclerosis, spinal cord injury,Parkinson's disease, epilepsy and vitamin deficiency. Neuropathic painis pathological as it has no protective role. It is often present wellafter the original cause has dissipated, commonly lasting for years,significantly decreasing a patient's quality of life (Woolf and Mannion,1999, Lancet, 353, 1959-1964). The symptoms of neuropathic pain aredifficult to treat, as they are often heterogeneous even betweenpatients with the same disease (Woolf & Decosterd, 1999, Pain Supp., 6,S141-S147; Woolf and Mannion, 1999, Lancet, 353, 1959-1964). Theyinclude spontaneous pain, which can be continuous, and paroxysmal orabnormal evoked pain, such as hyperalgesia (increased sensitivity to anoxious stimulus) and allodynia (sensitivity to a normally innocuousstimulus).

The inflammatory process is a complex series of biochemical and cellularevents, activated in response to tissue injury or the presence offoreign substances, which results in swelling and pain (Levine andTaiwo, 1994, Textbook of Pain, 45-56). Arthritic pain is the most commoninflammatory pain. Rheumatoid disease is one of the commonest chronicinflammatory conditions in developed countries and rheumatoid arthritisis a common cause of disability. The exact aetiology of rheumatoidarthritis is unknown, but current hypotheses suggest that both geneticand microbiological factors may be important (Grennan & Jayson, 1994,Textbook of Pain, 397-407). It has been estimated that almost 16 millionAmericans have symptomatic osteoarthritis (OA) or degenerative jointdisease, most of whom are over 60 years of age, and this is expected toincrease to 40 million as the age of the population increases, makingthis a public health problem of enormous magnitude (Houge & Mersfelder,2002, Ann Pharmacother., 36, 679-686; McCarthy et al., 1994, Textbook ofPain, 387-395). Most patients with osteoarthritis seek medical attentionbecause of the associated pain. Arthritis has a significant impact onpsychosocial and physical function and is known to be the leading causeof disability in later life. Ankylosing spondylitis is also a rheumaticdisease that causes arthritis of the spine and sacroiliac joints. Itvaries from intermittent episodes of back pain that occur throughoutlife to a severe chronic disease that attacks the spine, peripheraljoints and other body organs.

Another type of inflammatory pain is visceral pain which includes painassociated with inflammatory bowel disease (IBD). Visceral pain is painassociated with the viscera, which encompass the organs of the abdominalcavity. These organs include the sex organs, spleen and part of thedigestive system. Pain associated with the viscera can be divided intodigestive visceral pain and non-digestive visceral pain. Commonlyencountered gastrointestinal (GI) disorders that cause pain includefunctional bowel disorder (FBD) and inflammatory bowel disease (IBD).These GI disorders include a wide range of disease states that arecurrently only moderately controlled, including, in respect of FBD,gastro-esophageal reflux, dyspepsia, irritable bowel syndrome (IBS) andfunctional abdominal pain syndrome (FAPS), and, in respect of IBD,Crohn's disease, ileitis and ulcerative colitis, all of which regularlyproduce visceral pain. Other types of visceral pain include the painassociated with dysmenorrhea, cystitis and pancreatitis and pelvic pain.

It should be noted that some types of pain have multiple aetiologies andthus can be classified in more than one area, e.g. back pain and cancerpain have both nociceptive and neuropathic components.

Other types of pain include:

-   -   pain resulting from musculo-skeletal disorders, including        myalgia, fibromyalgia, spondylitis, sero-negative        (non-rheumatoid) arthropathies, non-articular rheumatism,        dystrophinopathy, glycogenolysis, polymyositis and pyomyositis;    -   heart and vascular pain, including pain caused by angina,        myocardical infarction, mitral stenosis, pericarditis, Raynaud's        phenomenon, scleredoma and skeletal muscle ischemia;    -   head pain, such as migraine (including migraine with aura and        migraine without aura), cluster headache, tension-type headache        mixed headache and headache associated with vascular disorders;        and    -   orofacial pain, including dental pain, otic pain, burning mouth        syndrome and temporomandibular myofascial pain.

The compounds of formula (I) are potentially useful in the treatment ofall kinds of pain but are particularly useful in the treatment ofneuropathic pain.

Apart from pain, the compounds of formula (I) are potentially useful inthe treatment of any disease or condition which is treatable using analpha-2-delta ligand. Such conditions include epilepsy, gastrointestinaldisorders, premature ejaculation, burning mouth syndrome, bladderdisorders (such as over active bladder), faintness attacks,fibromyalgia, hypokinesia, cranial disorders, hot flashes, essentialtremor, chemical dependencies and addictions, withdrawal symptomsassociated with dependencies or addictions, addictive behaviours,spasticity, arthritis, inflammatory disorders (e.g. rheumatoidarthritis, osteoarthritis, psoriasis), diuresis, premenstrual syndrome,premenstrual dysphoric disorder, tinnitus, gastric damage, Down'ssyndrome, demyelinating diseases (e.g. multiple sclerosis andamylolateral sclerosis), cerebral vascular disorders due to acute orchronic cerebrovascular damage (e.g. cerebral infarction, subarachnoidhaemorrhage or cerebral oedema), head trauma, spinal cord trauma andneuronal damage that occurs, for instance, during stroke, in cardiacbypass surgery, in incidents of intracranial hemorrhage, in perinatalasphyxia, in cardiac arrest and in status epilepticus. Alpha-2-deltaligands may also be useful in the treatment of delirium, dementia andamnestic and other cognitive or neurodegenerative disorders (e.g.Parkinson's disease, Huntington's disease, Alzheimer's disease, seniledementia, memory disorder, vascular dementia). They may be useful in thetreatment of movement disorders such as akinesias, dyskinesias,spasticities, Tourette's syndrome, Scott syndrome, palsys,akinetic-rigid syndrome and extra-pyramidal movement disorders. They mayalso be useful in the treatment of sleep disorders, mood disorders,depression, depressive disorders, bipolar disorders, anxiety disorders,panic, borderline personality disorder, schizophrenia, psychoticdisorders, behavioural disturbances associated with mental retardation,autistic disorder and conduct disorders.

All of the compounds of formula (I) can be prepared by conventionalroutes such as by the procedures described in the general methodspresented below or by the specific methods described in the Examplessection and the Preparations section, or by similar methods thereto. Thepresent invention also encompasses any one or more of these processesfor preparing the compounds of formula (I), in addition to any novelintermediates used therein.

In the following general methods, R¹, R², R³ and R⁴ are as previouslydefined for a compound of formula (I) unless otherwise stated and Ph isphenyl.

According to a first process, (A), a compound of formula (I), wherein R³and R⁴ are H, may be prepared by the hydrogenolytic deprotection of acompound of formula (III)

wherein R¹ and R² are as defined above. The hydrogenation is typicallycarried out using a source of hydrogen such as hydrogen gas,cyclohexadiene or ammonium formate (preferably hydrogen gas) and atransition metal catalyst such as a palladium, platinum or rhodiumcatalyst (preferably a palladium catalyst). An acid, such ashydrochloric or trifluoroacetic acid, may also be used to increase therate of reaction. In a preferred procedure, a solution of the compoundof formula (III) in a suitable solvent, such as ethanol, is treated withpalladium on carbon and hydrochloric acid hydrogenated at about 414 kPa(60 psi).

A compound of formula (III) may be prepared by treating an imine offormula (IV):

wherein R¹ is as defined above, with a compound of formula:R²M¹  (V)wherein R² is as defined above and M¹ is a suitable metal, optionallybearing one or more further ligands; or by treating an imine of formula(VI):

wherein R² is as defined above, with a compound of formula:R¹M¹  (VII)wherein R¹ and M¹ are as defined above. In such an imine additionreaction the organometallic reagent of formula (V) or (VII) is typicallyan organolithium or an organomagnesium derivative. An organomagensium(Grignard) reagent, wherein M¹ is MgX, X being a halide, is preferred.The reaction is carried out in a suitable inert solvent such astetrahydrofuran or diethyl ether at low temperature, typically between 0and −78° C. In a preferred procedure, a solution of the compound offormula (IV) or (VI) in a suitable solvent, such as tetrahydrofuran, istreated with a suitable Grignard reagent of formula (V) or (VII),respectively, at −50° C. and in the presence of boron trifluorideetherate.

Compounds of formula (IV) and (VI) can be prepared by the condensationof a compound of formula:

with, respectively, a compound of formula:

wherein R¹ is as defined above and X is C₁-C₆ alkyl; or a compound offormula (X):

wherein R² is as defined above and X is C₁-C₆ alkyl. The condensationmay be carried out under basic, neutral or acidic conditions andgenerally requires elevated temperatures and/or prolonged reactiontimes. In a typical procedure, a solution of the compound of formula(VII) and the compound of formula (IX) or (X), in a suitable solvent,such as trifluoroethanol, is heated at about 80° C. in the presence of adehydrating agent such as 4A molecular sieves.

Compounds of formula (X), (IX) and (VIII) are either commerciallyavailable or easily prepared by standard methods well known to theskilled person, either as a result of common general knowledge (e.g. see‘Comprehensive Organic Transformations’ by Richard Larock (1999, VCHPublishers Inc.) or by reference to specific published procedures.

Compounds of formula (I) wherein R³ and/or R⁴ are not H may be preparedfrom compounds of formula (I) wherein R³ and/or R⁴ are H by simplechemical transformations well known to the skilled man. Suitableconditions for such amide and ester forming reactions may be found inComprehensive Organic Transformations referenced above.

Alternatively, according to a second process, (B), a compound of formula(I), wherein R³ and R⁴ are H, may be prepared by hydrogenolyticdeprotection of a ring-opened compound of formula (IIIa)

wherein R¹ and R² are as defined above. The hydrogenation is typicallycarried out using a source of hydrogen such as hydrogen gas,cyclohexadiene or ammonium formate (preferably hydrogen gas) and atransition metal catalyst such as a palladium, platinum or rhodiumcatalyst (preferably a palladium catalyst). An acid, such ashydrochloric or trifluoroacetic acid, may also be used to increase therate of reaction. In a preferred procedure, a solution of the compoundof formula (IIIa) in a suitable solvent, such as propan-2-ol and water,is treated with palladium on carbon and hydrogenated at about 414 kPa(60 psi).

A compound of formula (IIIa) may be prepared by treating an imine offormula (IV) or (VI) with a compound of formula (V) or (VII) followed bytreatment with a suitable acid or base. Suitable conditions for such animine addition reaction are as described above for process (A). In apreferred procedure, a solution of the compound of formula (VI) in asuitable solvent, such as tetrahydrofuran, is first treated with asuitable Grignard reagent of formula (VII) at −78° C. in the presence ofboron trifluoride tetrahydrofuran complex, followed by treatment with asuitable acid such as aqueous hydrochloric acid.

According to a third process, (C), a compound of formula (I), wherein R³and R⁴ are both H, may alternatively be prepared by the hydrolysis of anitrile of formula (XI):

wherein R¹ and R² are as defined above. The hydrolysis is typicallyaccomplished with acidic or basic catalysis in an aqueous solvent at anelevated temperature. In a typical procedure, a solution of the compoundof formula (XI) in water is treated with 6 molar hydrochloric acid andheated to about 100° C.

A compound of formula (XI) may be prepared by the addition of cyanide toa compound of formula (XII):

wherein R¹ and R² are as defined above. A preferred source of cyanidefor the addition is a compound of formula M²CN wherein M² is a metalcation, optionally bearing other ligands. Most preferred is adialkylaluminium cyanide such as diethylaluminium cyanide. The reactionis carried out as a solution in a suitable inert solvent such astetrahydrofuran, dichloromethane or diethyl ether. In a preferredprocedure a solution of a compound of formula (XII) in a mixture ofisoproanol and tetrahydrofuran is treated with diethylaluminium cyanideat a temperature of between −78 and −20° C.

A compound of formula (XII) may be prepared by the reaction of acompound of formula (XIII)

with a compound of formula (XIV):

wherein R¹ and R² are as defined above, under dehydrating conditions.Typically the reaction is catalysed by a Lewis acid (e.g. titaniumtetraethoxide). In a preferred procedure, a solution of the compound offormula (XIII) and the compound of formula (XIV) in a suitable solvent(such as tetrahydrofuran) is treated with titanium tetraethoxide at atemperature of about 50° C.

Compounds of formula (XIII) and (XIV) are either commercially availableor easily prepared by standard methods well known to the skilled person,either as a result of common general knowledge (e.g. see ‘ComprehensiveOrganic Transformations’ by Richard Larock (1999, VCH Publishers Inc.)or by reference to specific published procedures.

According to a fourth process, (D), a compound of formula (I), whereinR³ and R⁴ are both H, may alternatively be prepared by the hydrolysis ofan ester of formula (XV):

wherein R¹ and R² are as defined above. The hydrolysis may be carriedout under acidic or basic conditions. In a typical procedure, a solutionof a compound of formula (XV) in aqueous hydrochloric acid is heatedunder reflux for 16 hours.

A compound of formula (XV) may be prepared by the methanolysis of acompound of formula (XVI):

wherein R¹ and R² are as defined above and Y¹ and Y² are each selectedfrom C₁-C₆ alkyl. The reaction may be carried out with acid or basecatalysis. In a typical procedure, a solution of a compound of formula(XVI) in methanolic hydrochloric acid is stirred at room temperature forabout 72 hours.

A compound of formula (XVI) may be prepared by the alkylation of acompound of formula (XVII):

wherein R¹, Y¹ and Y² are as defined above, with a compound of formulaR²L¹, wherein R² is as defined above and L¹ is a suitable leaving group.L¹ is preferably halo (particularly bromo), trifluoromethanesulphonateor methanesulphonate. Typically, the compound of formula (XVII) isdeprotonated with a base, such as butyl lithium, in an inert solventsuch as diethyl ether or tetrahydrofuran, at low temperature (usually inthe range −78 to −20° C.). A solution of the alkylating agent in aninert solvent is then added. In a preferred procedure, a solution of thecompound of formula (XVII) in tetrahydrofuran is treated with n-butyllithium at −78° C. and an excess of the alkylating agent is then added.

A compound of formula (XVII) may be prepared by the double alkylation ofa compound of formula (XVIII):

wherein R¹ is as defined above. Typically, the compound of formula(XVIII) is deprotonated using a base (e.g. potassium tert-butoxide,potassium hexamethyldisilazide or sodium hydride) in an inert solvent,such as tetrahydrofuran or diethyl ether. A suitable alkylating agent,such as an alkyl halide (particularly an alkyl bromide) or an alkylsulphonate ester (e.g. an alkyl mesylate) is then added at a temperatureof from −20° C. to room temperature. In a preferred procedure, an excessof trimethoxonium tetrafluoroborate in is used as the alkylating agent.

A compound of formula (XVIII) may be prepared by the cyclisation of acompound of formula (XIX):

wherein R¹ is as defined above. In a typical procedure, a solution of acompound of formula (XIX) in a suitable solvent, such as toluene, isheated under reflux.

A compound of formula (XIX) may be prepared by the reduction of acompound of formula (XX):

wherein R¹ is as defined above. The reduction is typically accomplishedusing hydrogen and a hydrogenation catalyst such as a palladium,platinum or rhodium catalyst. In a preferred procedure, a solution ofthe compound of formula (XX) in a suitable solvent, such as aqueousethanolic hydrochloric acid, is treated with hydrogen at roomtemperature.

A compound of formula (XX) may be prepared by coupling an amine offormula (XXI):

with an acid of formula (XXII):

wherein R¹ is as defined above. The acid is first activated, either byconversion to the corresponding acid chloride or by treatment with asuitable peptide coupling agent. If the acid chloride is used it ispreformed and then reacted with the amine as a solution in a suitableinert solvent (such as dichloromethane or tetrahydrofuran) in thepresence of a base (such as triethylamine). Alternatively, as solutionof the acid and the amine in a suitable solvent (such as dichloromethaneor tetrahydrofuran) is treated with a base (such as triethylamine) and acoupling agent (such as a carbodiimide).

Compounds of formula (XXI) and (XXII) are either commercially availableor easily prepared by standard methods well known to the skilled person,either as a result of common general knowledge (e.g. see ‘ComprehensiveOrganic Transformations’ by Richard Larock (1999, VCH Publishers Inc.)or by reference to specific published procedures.

According to a fifth process, (E), a compound of formula (I), wherein R³and R⁴ are both H, R¹ and R⁵ are not substituted by halo or cyano, andR² is methyl, may alternatively be prepared by resolution of a racemiccompound of formula (Ia).

Resolution may be carried out by a number of methods known to a personskilled in the art, including chiral chromatography, formation ofdiasteroemeric derivatives (such as esters, ethers or salts), orchemical or enzymatic kinetic resolution. Typically, a compound offormula (la) is treated with a chiral base or acid in a suitable organicsolvent to form diastereomeric salts and separation is achieved bycrystallisation of the least soluble diastereoisomer. Suitable resolvingagents include tartaric acid derivatives, mandelic acid, camphorsulfonicacid, sparteine, alpha-methylbenzylamine, pseudoephedrine andaminoalcohols. Diastereomeric salt resolution may also be used toincrease the enantiomeric excess of a non-racemic compound of formula(I).

A compound of formula (Ia), wherein R^(a) is aryl, optionallysubstituted with amino, (C₁-C₆)alkylamino, hydroxyl, (C₁-C₆)alkoxy,sulfonate, sulphonamide, sulfonyl, trifluoromethyl, nitro, (C₁-C₆)acylor nitrile, and R^(b) is hydrogen, (C₁-C₆)alkyl or R^(a), may beprepared from a compound of formula (XXIII) by hydrogenolyticdeprotection

Hydrogenolytic deprotection conditions are as described above forprocess (A).

Alternatively, a compound of formula (I) can be prepared from a compoundof formula (XXIII) by resolution of the compound of formula (XXIII)followed by hydrogenolytic deprotection.

A compound of formula (XXIII) may be prepared by treating a compound offormula (XXIV)

with a compound of formula (VII) as defined above. Suitable conditionsfor the imine addition reaction are as defined above for process (A). Anorganomagnesium (Grignard) reagent, wherein M¹ is MgX, X being a halide,is preferred. In a preferred procedure, a solution of the compound offormula (XXIV) in a suitable solvent, such as tetrahydrofuran, istreated with a suitable Grignard reagent of formula (VII) at lowtemperature, typically at a temperature of from 0 to −78° C. and in thepresence of boron trifluoride etherate or boron trifluoridetetrahydrofuran complex.

A compound of formula (XXIV) may be prepared by condensation of an estercompound of formula (X), as defined in process (A), with an aminecompound of formula (XXV) in the presence of a suitable catalyst.

Conditions are as described for process (A). Compounds of formula (XXV)are commercially available.

According to a sixth process (F), a compound of formula (I), wherein R³and R⁴ are both H, R¹ and R⁵ are not substituted by halo or cyano, andR² is methyl, may be alternatively prepared by deprotection of acompound of formula (XXVI)

wherein R^(a) and R^(b) are as defined for process (E) and R^(c) is asuitable chiral ester group, such as mentyl or pseudoephidrinyl. Thedeprotection may be carried out under acidic or basic conditions,typically aqueous hydrochloric acid and diethyl ether or aqueous citricacid and tetrahydrofuran.

Compounds of formula (XXVI) may be prepared as described in Tetrahedron:Asymmetry, 1992, 3, 591-594 and Tetrahedron Letters, 1982, 23,4259-4262.

Alternatively, a racemic compound of formula (Ia) may be prepared by ananalogous process wherein R^(c) is an achiral ester group such as C₁₋₆alkyl or benzyl.

A compound of formula (XXVI) may be prepared by reaction of a compoundof formula (XXVII) with an electrophile of formula (XXVIII) under basicconditions

wherein LG is a suitable leaving group such as Cl, Br, I, or R^(d)SO₂Owherein R^(d) is C₁-C₆ alkyl, CF₃, or aryl optionally substituted withC₁-C₆ alkyl or nitro, preferably Br or trifluoromethanesulfonyl.Additionally, an additive such as potassium iodide may be used to form amore reactive electrophile in-situ. Typically the reaction is carriedout using an inorganic base such as potassium carbonate or sodiumhydroxide, or an organic base such as a phosphazene base, optionally inthe presence of a phase transfer catalyst, in an organic solvent such asdichloromethane, tetrahydrofuran or toluene at a temperature of from−78° C. to room temperature.

Compounds of the formula (XXVII) may be prepared as described inTetrahedron, 2004, 60, 5919-5930 and Tetrahedron Letters, 1998, 39,8775-8778.

A compound of formula (XXVII) may also be prepared by isomerisation of acompound of formula (XXIV) which itself is prepared from an aminecompound of formula (XXV) by a process analogous to that described inprocess (E).

Alternatively, a compound of formula (XXVI) may be prepared bymethylation of a compound of formula (XXIX)

Typical conditions comprise treating a compound of formula (XXIX) with asuitable electrophile (e.g. methyl iodide, dimethyl sulfate,trimethyloxonium tetrafluoroborate, or methyl triflate) and an inorganicbase, such as potassium carbonate or sodium hydroxide, or an organicbase, such as a phosphazene base, optionally in the presence of a phasetransfer catalyst, in an organic solvent, such as dichloromethane,tetrahydrofuran or toluene, at a temperature of from −78° C. to roomtemperature.

A compound of formula (XXIX) may be prepared by reaction of a compoundof formula (XXX) with an electrophile of formula (XXVIII) under basicconditions as described above for process (F).

Alternatively, compounds of the formula (XXIX) may be prepared asdescribed in Tetrahedron, 2004, 60, 5919-5930 and Tetrahedron Letters,1998, 39, 8775-8778.

Compounds of the formula (XXX) may be prepared as described in J. Org.Chem, 1982, 47, 2663-2666.

According to a seventh process (G), a racemic compound of formula (Ia)wherein R³ and R⁴ are both H, R¹ and R⁵ are not substituted by halo orcyano, and R² is methyl, may be alternatively prepared by condensationof a compound of formula (XXXI) with an ammonium source or amine and acyanide source, followed by hydrolysis of the resulting aminonitrile orhydantoin.

The condensation may be carried out using an ammonia source such asammonium acetate or ammonium carbonate, or an amine R^(e)NH₂, whereinR^(e) is C₁-C₆ alkyl, benzyl, or aryl optionally substituted with amino,(C₁-C₆ alkyl)amino, hydroxyl, C₁-C₆ alkoxy, sulfonate, sulfonamido,sulfonyl, CF₃, nitro, C₁-C₆ acyl or nitrile, and an acyl anionequivalent such as a cyanide salt. Typical conditions for hydrolysiscomprise treating the resulting aminonitrile or hydantoin with eitheracid or base in an aqueous solvent system. Typically the aminonitrile orhydantoin is treated with aqueous hydrochloric, hydrobromic, sulphuricor phosphoric acid, or aqueous potassium hydroxide or sodium hydroxidecontaining 6 to 12% hydrogen peroxide, at a temperature of from roomtemperature to 100° C.

Alternatively, the condensation step may be carried out either on theketone or on a suitable ketone derivative such as a phosphinylimine inthe presence of a chiral catalyst (such as a lanthanide-BINOL derivedcatalyst or a cyclohexyldiamine derived catalyst) or a chiral ketonederivative of the compound of formula (XXXI), such as a chiral imine, orsulfinylimine, may be used to provide a compound of formula (I) in astereoselective manner.

According to an eighth process, (H), a compound of formula (I) whereinR³ and R⁴ are both H, R¹ and R⁵ are not substituted by halo or cyano,and R² is methyl, may be alternatively prepared by Hoffmannrearrangement of a compound of formula (XXXII)

wherein R^(f) is H, C₁-C₁₀ alkyl, benzyl or substituted benzyl. TheHoffmann rearrangement is suitably carried out using sodium hypobromiteor a mixture of aqueous sodium hydroxide and bromine. Alternatively,phenyliodosylbis(triflate) in a mixture of acetonitrile and water atroom temperature will effect this transformation.

A compound of formula (XXXII) may be prepared by desymmetrisation of acompound of formula (XXXIII)

wherein R^(f) is as defined aboveor a compound of formula (XXXV)

by selective reaction of one of the ester groups with ammonia or anammonia source such as ammonium chloride, or a suitably protected aminefollowed by deprotection. Alternatively, the desymmetrisation may beeffected by hydrolysis of one of the ester groups to the carboxylic acidfollowed by amide coupling (for example using 1,1′-carbonyl diimidazoleand ammonia in acetonitrile at room temperature) to give a compound offormula (XXXII) (see Angewandte Chemie, International Edition (2004),43(47), 6493-6496). The desymmetrisation may be carried out either usingan enzyme (for example a lipase such as pig liver esterase or CandidaAntarctica in an aqueous or ammonia based solvent system) or chemically(for example using alpha-methyl benzylamine followed by hydrogenolysisusing palladium on carbon and hydrogen in an alcoholic solvent at roomtemperature or above, or using a chiral catalyst and a suitable amine orammonia source).

Compounds of formula (XXXIII) and (XXXV) can be prepared fromcommercially available compounds of formula (XXXIV) by reaction withsuitable electrophiles of formula (XXVIII) under basic conditions asdescribed in procedure F

wherein R^(g) is H, C₁-C₁₀ alkyl, benzyl or substituted benzyl, or thetwo R^(g) groups taken together are C(CH₃)₂.

Alternatively, compounds of formula (XXXIII) and (XXXV) can be preparedfrom commercially available compounds of formula (XXXVI)

wherein R^(g) is as defined above, by reaction with suitableelectrophiles of formula (XXVIII) under basic conditions followed bymethylation with a suitable reagent as described in procedure F.

Alternatively, a compound of formula (Ia) can be prepared by Hoffmanrearrangement of a compound (XXXIIa)

wherein R^(f) is as defined above. Conditions are as described forprocess (H) above.

Racemic compounds of formula (XXXIIa) can be prepared from compounds offormula (XXXIII) or (XXXV) using the conditions described for process(H) above, but in the absence of an enantioselective catalyst or chiralreagent.

Compounds of formula (I) can also be prepared by using the reactionsdescribed above to construct a compound wherein R¹ or R² are partiallyformed and then completing the synthesis by functional groupmanipulation. For instance, a group may be carried through the synthesisin a protected form and deprotected in a final step. Suitable protectinggroups are described in ‘Protective Groups in Organic Synthesis’ byTheodora Greene and Peter Wuts (third edition, 1999, John Wiley andSons). Suitable functional group transformations are described in‘Comprehensive Organic Transformations’ by Richard Larock (1999, VCHPublishers Inc.).

Compounds of formula (I) may be administered as crystalline or amorphousproducts. They may be obtained, for example, as solid plugs, powders, orfilms by methods such as precipitation, crystallization, freeze drying,spray drying, or evaporative drying. Microwave or radio frequency dryingmay be used for this purpose.

They may be administered alone or in combination with one or more othercompounds of formula (I) or in combination with one or more other drugs(or as any combination thereof). Generally, they will be administered asa formulation in association with one or more pharmaceuticallyacceptable excipients. The term ‘excipient’ is used herein to describeany ingredient other than a compound of formula (I). The choice ofexcipient will to a large extent depend on factors such as theparticular mode of administration, the effect of the excipient onsolubility and stability, and the nature of the dosage form.

Pharmaceutical compositions suitable for the delivery of compounds offormula (I) and methods for their preparation will be readily apparentto those skilled in the art. Such compositions and methods for theirpreparation may be found, for example, in Remington's PharmaceuticalSciences, 19th Edition (Mack Publishing Company, 1995).

A compound of formula (I) may be administered orally. Oraladministration may involve swallowing, so that the compound enters thegastrointestinal tract, or buccal or sublingual administration may beemployed by which the compound enters the blood stream directly from themouth.

Formulations suitable for oral administration include solid formulationssuch as tablets, capsules containing particulates, liquids, powders,lozenges (including liquid-filled lozenges), chews, multi- andnano-particulates, gels, solid solutions, liposomes, films, ovules,sprays and liquid formulations.

Liquid formulations include suspensions, solutions, syrups and elixirs.Such formulations may be employed as fillers in soft or hard capsulesand typically comprise a carrier, for example, water, ethanol,polyethylene glycol, propylene glycol, methylcellulose or a suitableoil, and one or more emulsifying agents and/or suspending agents. Liquidformulations may also be prepared by the reconstitution of a solid, forexample, from a sachet.

A compound of formula (I) may also be used in fast-dissolving,fast-disintegrating dosage forms such as those described in ExpertOpinion in Therapeutic Patents, 11 (6), 981-986, by Liang and Chen(2001).

For tablet dosage forms, depending on dose, a compound of formula (I)may make up from 1 weight % to 80 weight % of the dosage form, moretypically from 5 weight % to 60 weight % of the dosage form. In additionto the compound of formula (I), tablets generally contain adisintegrant. Examples of disintegrants include sodium starch glycolate,sodium carboxymethyl cellulose, calcium carboxymethyl cellulose,croscarmellose sodium, crospovidone, polyvinylpyrrolidone, methylcellulose, microcrystalline cellulose, lower alkyl-substitutedhydroxypropyl cellulose, starch, pregelatinised starch and sodiumalginate. Generally, the disintegrant will comprise from 1 weight % to25 weight %, preferably from 5 weight % to 20 weight % of the dosageform.

Binders are generally used to impart cohesive qualities to a tabletformulation. Suitable binders include microcrystalline cellulose,gelatin, sugars, polyethylene glycol, natural and synthetic gums,polyvinylpyrrolidone, pregelatinised starch, hydroxypropyl cellulose andhydroxypropyl methylcellulose. Tablets may also contain diluents, suchas lactose (as, for example, the monohydrate, spray-dried monohydrate oranhydrous form), mannitol, xylitol, dextrose, sucrose, sorbitol,microcrystalline cellulose, starch and dibasic calcium phosphatedihydrate.

Tablets may also optionally comprise surface active agents, such assodium lauryl sulfate and polysorbate 80, and glidants such as silicondioxide and talc. When present, surface active agents may comprise from0.2 weight % to 5 weight % of the tablet, and glidants may comprise from0.2 weight % to 1 weight % of the tablet.

Tablets also generally contain lubricants such as magnesium stearate,calcium stearate, zinc stearate, sodium stearyl fumarate, and mixturesof magnesium stearate with sodium lauryl sulphate. Lubricants generallycomprise from 0.25 weight % to 10 weight %, preferably from 0.5 weight %to 3 weight % of the tablet.

Other possible ingredients include anti-oxidants, colourants, flavouringagents, preservatives and taste-masking agents.

Exemplary tablets contain up to about 80% of a compound of formula (I),from about 10 weight % to about 90 weight % binder, from about 0 weight% to about 85 weight % diluent, from about 2 weight % to about 10 weight% disintegrant, and from about 0.25 weight % to about 10 weight %lubricant.

Tablet blends may be compressed directly or by roller to form tablets.Tablet blends or portions of blends may alternatively be wet-, dry-, ormelt-granulated, melt congealed, or extruded before tabletting. Thefinal formulation may comprise one or more layers and may be coated oruncoated; it may even be encapsulated.

The formulation of tablets is discussed in Pharmaceutical Dosage Forms:Tablets, Vol. 1, by H. Lieberman and L. Lachman (Marcel Dekker, NewYork, 1980).

Consumable oral films for human or veterinary use are typically pliablewater-soluble or water-swellable thin film dosage forms which may berapidly dissolving or mucoadhesive and typically comprise a compound offormula (I), a film-forming polymer, a binder, a solvent, a humectant, aplasticiser, a stabiliser or emulsifier, a viscosity-modifying agent anda solvent. Some components of the formulation may perform more than onefunction.

A compound of formula (I) for use in a film may be water-soluble orinsoluble. A water-soluble compound typically comprises from 1 weight %to 80 weight %, more typically from 20 weight % to 50 weight %, of thesolutes. Less soluble compounds may comprise a greater proportion of thecomposition, typically up to 88 weight % of the solutes. Alternatively,a compound of formula (I) may be used in the form of multiparticulatebeads.

The film-forming polymer may be selected from natural polysaccharides,proteins, or synthetic hydrocolloids and is typically present in therange 0.01 to 99 weight %, more typically in the range 30 to 80 weight%.

Other possible ingredients in such a film include anti-oxidants,colorants, flavourings, flavour enhancers, preservatives, salivarystimulating agents, cooling agents, co-solvents (including oils),emollients, bulking agents, anti-foaming agents, surfactants andtaste-masking agents.

Films in accordance with the invention are typically prepared byevaporative drying of thin aqueous films coated onto a peelable backingsupport or paper. This may be done in a drying oven or tunnel, typicallya combined coater dryer, or by freeze-drying or vacuuming.

Solid formulations for oral administration may be formulated to beimmediate and/or modified release. Modified release formulations includedelayed, sustained, pulsed, controlled, targeted and programmed releaseformulations.

Suitable modified release formulations for the purposes of the inventionare described in U.S. Pat. No. 6,106,864. Details of other suitablerelease technologies such as high energy dispersions and osmotic andcoated particles are to be found in Pharmaceutical Technology On-line,25(2), 1-14, by Verma et al (2001). The use of chewing gum to achievecontrolled release is described in WO-A-00/35298.

A compound of formula (I) may also be administered directly into theblood stream, into muscle, or into an internal organ. Suitable routesfor such parenteral administration include intravenous, intraarterial,intraperitoneal, intrathecal, intraventricular, intraurethral,intrasternal, intracranial, intramuscular and subcutaneous delivery.Suitable means for parenteral administration include needle (includingmicroneedle) injectors, needle-free injectors and infusion techniques.

Parenteral formulations are typically aqueous solutions which maycontain excipients such as salts, carbohydrates and buffering agents(preferably at a pH of from 3 to 9), but, for some applications, theymay be more suitably formulated as a sterile non-aqueous solution or asa dried form to be used in conjunction with a suitable vehicle such assterile, pyrogen-free water.

The preparation of parenteral formulations under sterile conditions, forexample, by lyophilisation, may readily be accomplished using standardpharmaceutical techniques well known to those skilled in the art.

The solubility of a compound of formula (I) used in the preparation of aparenteral formulation may be increased by the use of appropriateformulation techniques, such as the incorporation ofsolubility-enhancing agents.

Formulations for parenteral administration may be formulated to beimmediate and/or modified release. Modified release formulations includedelayed, sustained, pulsed, controlled, targeted and programmed releaseformulations. Thus, a compound of formula (I) may be formulated as asolid, semi-solid, or thixotropic liquid for administration as animplanted depot providing modified release of the active compound.Examples of such formulations include drug-coated stents andpoly(dl-lactic-coglycolic)acid (PGLA) microspheres.

A compound of formula (I) may also be administered topically to the skinor mucosa, i.e. dermally or transdermally. Typical formulations for thispurpose include gels, hydrogels, lotions, solutions, creams, ointments,dusting powders, dressings, foams, films, skin patches, wafers,implants, sponges, fibres, bandages and microemulsions. Liposomes mayalso be used. Typical carriers include alcohol, water, mineral oil,liquid petrolatum, white petrolatum, glycerin, polyethylene glycol andpropylene glycol. Penetration enhancers may be incorporated—see, forexample, J. Pharm. Sci., 88 (10), 955-958, by Finnin and Morgan (October1999).

Other means of topical administration include delivery byelectroporation, iontophoresis, phonophoresis, sonophoresis andmicroneedle or needle-free (e.g. Powderject™, Bioject™, etc.) injection.

Formulations for topical administration may be formulated to beimmediate and/or modified release. Modified release formulations includedelayed, sustained, pulsed, controlled, targeted and programmed releaseformulations.

A compound of formula (I) can also be administered intranasally or byinhalation, typically in the form of a dry powder (either alone, as amixture, for example, in a dry blend with lactose, or as a mixedcomponent particle, for example, mixed with phospholipids, such asphosphatidylcholine) from a dry powder inhaler or as an aerosol sprayfrom a pressurised container, pump, spray, atomiser (preferably anatomiser using electrohydrodynamics to produce a fine mist), ornebuliser, with or without the use of a suitable propellant, such as1,1,1,2-tetrafluoroethane or 1,1,1,2,3,3,3-heptafluoropropane. Forintranasal use, the powder may comprise a bioadhesive agent, forexample, chitosan or cyclodextrin.

The pressurised container, pump, spray, atomizer, or nebuliser containsa solution or suspension of a compound of formula (I) comprising, forexample, ethanol, aqueous ethanol, or a suitable alternative agent fordispersing, solubilising, or extending release of the active, apropellant(s) as solvent and an optional surfactant, such as sorbitantrioleate, oleic acid, or an oligolactic acid.

Prior to use in a dry powder or suspension formulation, a drug productis micronised to a size suitable for delivery by inhalation (typicallyless than 5 microns). This may be achieved by any appropriatecomminuting method, such as spiral jet milling, fluid bed jet milling,supercritical fluid processing to form nanoparticles, high pressurehomogenisation, or spray drying.

Capsules (made, for example, from gelatin orhydroxypropylmethylcellulose), blisters and cartridges for use in aninhaler or insufflator may be formulated to contain a powder mix of acompound of formula (I), a suitable powder base such as lactose orstarch and a performance modifier such as l-leucine, mannitol, ormagnesium stearate. The lactose may be anhydrous or in the form of themonohydrate, preferably the latter. Other suitable excipients includedextran, glucose, maltose, sorbitol, xylitol, fructose, sucrose andtrehalose.

A suitable solution formulation for use in an atomiser usingelectrohydrodynamics to produce a fine mist may contain from 1 μg to 20mg of a compound of formula (I) per actuation and the actuation volumemay vary from 1 μl to 100 μl. A typical formulation may comprise acompound of formula (I), propylene glycol, sterile water, ethanol andsodium chloride. Alternative solvents which may be used instead ofpropylene glycol include glycerol and polyethylene glycol.

Suitable flavours, such as menthol and levomenthol, or sweeteners, suchas saccharin or saccharin sodium, may be added to those formulationsintended for inhaled/intranasal administration.

Formulations for inhaled/intranasal administration may be formulated tobe immediate and/or modified release using, for example, PGLA. Modifiedrelease formulations include delayed, sustained, pulsed, controlled,targeted and programmed release formulations.

In the case of dry powder inhalers and aerosols, the dosage unit isdetermined by means of a valve which delivers a metered amount. Units inaccordance with the invention are typically arranged to administer ametered dose or “puff”. The overall daily dose will be administered in asingle dose or, more usually, as divided doses throughout the day.

A compound of formula (I) may be administered rectally or vaginally,e.g. in the form of a suppository, pessary, or enema. Cocoa butter is atraditional suppository base, but various alternatives may be used asappropriate.

Formulations for rectal/vaginal administration may be formulated to beimmediate and/or modified release. Modified release formulations includedelayed, sustained, pulsed, controlled, targeted and programmed releaseformulations.

A compound of formula (I) may also be administered directly to the eyeor ear, typically in the form of drops of a micronised suspension orsolution in isotonic, pH-adjusted, sterile saline. Other formulationssuitable for ocular and aural administration include ointments,biodegradable (e.g. absorbable gel sponges, collagen) andnon-biodegradable (e.g. silicone) implants, wafers, lenses andparticulate or vesicular systems, such as niosomes or liposomes. Apolymer such as crossed-linked polyacrylic acid, polyvinylalcohol,hyaluronic acid, a cellulosic polymer, for example,hydroxypropylmethylcellulose, hydroxyethylcellulose, or methylcellulose, or a heteropolysaccharide polymer, for example, gelan gum,may be incorporated together with a preservative, such as benzalkoniumchloride. Such formulations may also be delivered by iontophoresis.

Formulations for ocular/aural administration may be formulated to beimmediate and/or modified release. Modified release formulations includedelayed, sustained, pulsed, controlled, targeted, or programmed releaseformulations.

A compound of formula (I) may be combined with a soluble macromolecularentity, such as a cyclodextrin or a suitable derivative thereof or apolyethylene glycol-containing polymer, in order to improve itssolubility, dissolution rate, taste-masking, bioavailability and/orstability in any of the aforementioned modes of administration.

Drug-cyclodextrin complexes, for example, are found to be generallyuseful for most dosage forms and administration routes. Both inclusionand non-inclusion complexes may be used. As an alternative to directcomplexation with the drug, the cyclodextrin may be used as an auxiliaryadditive, i.e. as a carrier, diluent, or solubiliser. Most commonly usedfor these purposes are alpha-, beta- and gamma-cyclodextrins, examplesof which may be found in International Patent Applications Nos.WO-A-91/11172, WO-A-94/02518 and WO-A-98/55148.

For administration to human patients, the total daily dose of a compoundof formula (I) is typically in the range of from 1 mg to 1000 mgdepending, of course, on the mode of administration and the potency ofthe selected compound. The total daily dose may be administered insingle or divided doses and may, at the physician's discretion, falloutside of the typical range given herein.

These dosages are based on an average human subject having a weight ofabout 60 kg to 70 kg. The physician will readily be able to determinedoses for subjects whose weight falls outside this range, such asinfants and the elderly.

For the avoidance of doubt, references herein to “treatment” includereferences to curative, palliative and prophylactic treatment.

The biological activity of the alpha-2-delta ligands of the inventionmay be measured in a radioligand binding assay using [³H]gabapentin andthe α₂δ subunit derived from porcine brain tissue based on the methodgiven in J. Biol. Chem., 1996, 271(10), 5768-5776). This assay isreproduced below.

[³H]Gabapentin Binding Assay

Preparation of Brain Membranes

All solutions were maintained at 4° C. throughout. Pig brain cortex (upto 50 g) (fresh or frozen) was homogenised in 10 volumes of Buffer A(0.32 M Sucrose/1 mM EDTA/1 mM EGTA/10 mM Hepes/KOH, pH 7.4) by sixstrokes of a glass/teflon homogeniser at 600 r.p.m. After removal of the1000 g×10 minute pellet, the supernatant was centrifuged at 40,000 g for20 minutes and the resulting pellet was resuspended in 10 volumes ofBuffer B (1 mM EDTA/1 mM EGTA/10 mM Hepes/KOH, pH 7.4). Following 30minutes of continuous stirring, membranes were pelleted as above twicemore by centrifugation with Buffer B, before a final re-suspension inapproximately 3 volumes of storage buffer (1.25 mM EDTA/1.25 mM EGTA/25%Glycerol/12.5 mM Hepes/KOH, pH 7.4) to give a concentration of about 3milligrams of protein per millilitre. Aliquots were stored at −80° C.until required.

Binding Assay Protocol:

Binding of [³H]gabapentin to pig cerebral cortex membranes was carriedout at 22° C. in 10 mM Hepes/KOH, pH 7.4 for 60 minutes. Non-specificbinding (nsb) was defined as the binding obtained in the presence of 10μM pregabalin. An assay volume of 250 μl was employed, comprising 200 μlof membranes, 25 μl test compound/buffer/nsb, 25 μl [³H]gabapentin(final assay concentration ˜10 nM). Separation of unbound radioligandwas effected by rapid filtration under vacuum through cold 50 mMTris/HCl, pH 7.4-dipped GF/B unifilter plates, using 2×1 ml of cold 50mM Tris/HCl, pH 7.4. Plates were left to dry before addition of 50μl/well microscint-40 and the amount of radioactivity bound determinedusing a TopCount scintillation counter. Results may be expressed as anIC₅₀ in terms of μM or nM.

All the Examples described below were tested in this alpha-2-delta assayand were found to have a binding affinity (IC₅₀) of 1 μM or less. Forinstance, (2S)-2-amino-4-ethyl-2-methylhexanoic acid (Example 1) had abinding affinity of 21 nM.

An alpha-2-delta receptor ligand may be usefully combined with anotherpharmacologically active compound, or with two or more otherpharmacologically active compounds, particularly in the treatment ofpain. For example, an alpha-2-delta receptor ligand, particularly acompound of formula (I), or a pharmaceutically acceptable salt orsolvate thereof, as defined above, may be administered simultaneously,sequentially or separately in combination with one or more agentsselected from:

-   -   an opioid analgesic, e.g. morphine, heroin, hydromorphone,        oxymorphone, levorphanol, levallorphan, methadone, meperidine,        fentanyl, cocaine, codeine, dihydrocodeine, oxycodone,        hydrocodone, propoxyphene, nalmefene, nalorphine, naloxone,        naltrexone, buprenorphine, butorphanol, nalbuphine or        pentazocine;    -   a nonsteroidal antiinflammatory drug (NSAID), e.g. aspirin,        diclofenac, diflusinal, etodolac, fenbufen, fenoprofen,        flufenisal, flurbiprofen, ibuprofen, indomethacin, ketoprofen,        ketorolac, meclofenamic acid, mefenamic acid, nabumetone,        naproxen, oxaprozin, phenylbutazone, piroxicam, sulindac,        tolmetin or zomepirac;    -   a barbiturate sedative, e.g. amobarbital, aprobarbital,        butabarbital, butabital, mephobarbital, metharbital,        methohexital, pentobarbital, phenobartital, secobarbital,        talbutal, theamylal or thiopental;    -   a benzodiazepine having a sedative action, e.g.        chlordiazepoxide, clorazepate, diazepam, flurazepam, lorazepam,        oxazepam, temazepam or triazolam;    -   an H₁ antagonist having a sedative action, e.g. diphenhydramine,        pyrilamine, promethazine, chlorpheniramine or chlorcyclizine;    -   a sedative such as glutethimide, meprobamate, methaqualone or        dichloralphenazone;    -   a skeletal muscle relaxant, e.g. baclofen, carisoprodol,        chlorzoxazone, cyclobenzaprine, methocarbamol or orphrenadine;    -   an NMDA receptor antagonist, e.g. dextromethorphan        ((+)-3-hydroxy-N-methylmorphinan) or its metabolite dextrorphan        ((+)-3-hydroxy-N-methylmorphinan), ketamine, memantine,        pyrroloquinoline quinone or        cis-4-(phosphonomethyl)-2-piperidinecarboxylic acid;    -   an alpha-adrenergic, e.g. doxazosin, tamsulosin, clonidine or        4-amino-6,7-dimethoxy-2-(5-methanesulfonamido-1,2,3,4-tetrahydroisoquinol-2-yl)-5-(2-pyridyl)        quinazoline;    -   a tricyclic antidepressant, e.g. desipramine, imipramine,        amytriptiline or nortriptiline;    -   an anticonvulsant, e.g. carbamazepine or valproate;    -   a tachykinin (NK) antagonist, particularly an NK-3, NK-2 or NK-1        antagonist, e.g.        (αR,9R)-7-[3,5-bis(trifluoromethyl)benzyl]-8,9,10,11-tetrahydro-9-methyl-5-(4-methylphenyl)-7H-[1,4]diazocino[2,1-g][1,7]naphthridine-6-13-dione        (TAK-637),        5-[[(2R,3S)-2-[(1R]-1-[3,5-bis(trifluoromethyl)phenyl]ethoxy-3-(4-fluorophenyl)-4-morpholinyl]methyl]-1,2-dihydro-3H-1,2,4-triazol-3-one        (MK-869), lanepitant, dapitant or        3-[[2-methoxy-5-(trifluoromethoxy)phenyl]methylamino]-2-phenyl-piperidine        (2S,3S);    -   a muscarinic antagonist, e.g. oxybutin, tolterodine,        propiverine, tropsium chloride or darifenacin;    -   a selective COX-2 inhibitor, e.g. celecoxib, rofecoxib or        valdecoxib;    -   a non-selective COX inhibitor (preferably with GI protection),        e.g. nitroflurbiprofen (HCT-1026);    -   a coal-tar analgesic, in particular paracetamol;    -   a neuroleptic such as droperidol;    -   a vanilloid receptor agonist (e.g. resinferatoxin) or antagonist        (e.g. capsazepine);    -   a beta-adrenergic such as propranolol;    -   a local anaesthetic such as mexiletine;    -   a corticosteriod such as dexamethasone;    -   a 5-HT receptor agonist or antagonist, particularly a        5-HT_(1B/1D) agonist such as eletriptan, sumatriptan,        naratriptan, zolmitriptan or rizatriptan;    -   a cholinergic (nicotinic) analgesic;    -   Tramadol (trade mark);    -   a PDEV inhibitor, such as sildenafil, vardenafil, taladafil,        5-[2-ethoxy-5-(4-ethylpiperazin-1-ylsulphonyl)pyridin-3-yl]-3-ethyl-2-[2-methoxyethyl]-2,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one,        5-(5-acetyl-2-butoxy-3-pyridinyl)-3-ethyl-2-(1-ethyl-3-azetidinyl)-2,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one,        1-{6-ethoxy-5-[3-ethyl-6,7-dihydro-2-(2-methoxyethyl)-7-oxo-2H-pyrazolo[4,3-d]pyrimidin-5-yl]-3-pyridylsulfonyl}-4-ethylpiperazine,        or        N-[1-(2-ethoxyethyl)-5-(N-ethyl-N-methylamino)-7-(4-methylpyridin-2-ylamino)-1H-pyrazolo[4,3-d]pyrimidine-3-carbonyl]methanesulfonamide;    -   a canabinoid;    -   metabotropic glutamate subtype 1 receptor (mGluR1) antagonist;    -   a serotonin reuptake inhibitor such as sertraline;    -   a noradrenaline reuptake inhibitor, especially a selective        noradrenaline reuptake inhibitor such as (S,S)-reboxetine;    -   an inducible nitric oxide synthase (iNOS) inhibitor such as        S-[2-[(1-iminoethyl)amino]ethyl]-2-methyl-L-cysteine or        (2S,5Z)-2-amino-2-methyl-7-[(1-iminoethyl)amino]-5-heptenoic        acid;    -   an acetylcholine esterase inhibitor such as donepezil;    -   a dopamine type 2 (D2) antagonist such as ziprazidone;    -   an prostaglandin E₂ subtype 4 (EP4) antagonist such as        N-[({2-[4-(2-ethyl-4,6-dimethyl-1H-imidazo[4,5-c]pyridin-1-yl)phenyl]ethyl}amino)carbonyl]-4-methylbenzenesulfonamide        or        4-[(1S)-1-({[5-chloro-2-(3-fluorophenoxy)pyridin-3-yl]carbonyl}amino)ethyl]benzoic        acid;        and the pharmaceutically acceptable salts and solvates thereof.

Where a combination of active compounds is to be administered, two ormore pharmaceutical compositions may conveniently be combined in theform of a kit suitable for co-administration of the compositions.

Such a kit comprises two or more separate pharmaceutical compositions,at least one of which contains an alpha-2-delta receptor antagonist,particularly a compound of formula (I), and means for separatelyretaining said compositions, such as a container, divided bottle, ordivided foil packet. An example of such a kit is the familiar blisterpack used for the packaging of tablets, capsules and the like.

Such a kit is particularly suitable for administering different dosageforms, for example, oral and parenteral formulations, for administeringseparate compositions at different dosage intervals, or for titratingseparate compositions against one another. To assist compliance, the kittypically comprises directions for administration and may be providedwith a so-called memory aid.

It will be appreciated that what the invention provides, and what willbe claimed, is as follows:

-   -   (i) a compound of formula (II) or a pharmaceutically acceptable        salt or solvate thereof;    -   (ii) a process for the preparation of a compound of formula (I)        or a pharmaceutically acceptable salt or solvate thereof;    -   (iii) a pharmaceutical composition including a compound of        formula (II) or a pharmaceutically acceptable salt or solvate        thereof, together with a pharmaceutically acceptable excipient;    -   (iv) a compound of formula (II) or a pharmaceutically acceptable        salt, solvate or composition thereof, for use as a medicament;    -   (v) the use of a compound of formula (I) or of a        pharmaceutically acceptable salt, solvate or composition        thereof, for the manufacture of a medicament to treat a disease        for which an alpha-2-delta receptor ligand is indicated;    -   (vi) the use of a compound of formula (I) or of a        pharmaceutically acceptable salt, solvate or composition        thereof, for the manufacture of a medicament for the treatment        of pain;    -   (vii) a method of treatment of a mammal, including a human        being, with an alpha-2-delta receptor ligand, including treating        said mammal with an effective amount of a compound of        formula (I) or with a pharmaceutically acceptable salt, solvate        or composition thereof;    -   (viii) a method of treatment of a mammal, including a human        being, to treat pain, including treating said mammal with an        effective amount of a compound of formula (I) or with a        pharmaceutically acceptable salt, solvate or composition        thereof;    -   (ix) certain novel intermediates disclosed herein; and    -   (x) a combination of a compound of formula (I) or (II) and one        or more further pharmacologically active compounds.

The following Examples illustrate the preparation of compounds offormula (I).

¹H Nuclear magnetic resonance (NMR) spectra were in all cases consistentwith the proposed structures. Characteristic chemical shifts (8) aregiven in parts-per-million downfield from tetramethylsilane usingconventional abbreviations for designation of major peaks: e.g. s,singlet; d, doublet; t, triplet; q, quartet; m, multiplet; br, broad.The mass spectra (MS) were recorded using either electrospray ionisation(ESI) or atmospheric pressure chemical ionisation (APCI). The followingabbreviations have been used for common solvents: CDCl₃,deuterochloroform; D₆-DMSO, deuterodimethylsulphoxide; CD₃OD,deuteromethanol; THF, tetrahydrofuran. ‘Ammonia’ refers to aconcentrated solution of ammonia in water possessing a specific gravityof 0.88. Where thin layer chromatography (TLC) has been used it refersto silica gel TLC using silica gel 60 F₂₅₄ plates, R_(f) is the distancetravelled by a compound divided by the distance travelled by the solventfront on a TLC plate. Microwave radiation was performed using machineswith a power range of 15 to 300 W at 2.45 GHz, the actual power suppliedvarying during the course of the reaction to maintain a constanttemperature. LCMS indicates liquid chromatography mass spectrometry(R_(t)=retention time).

EXAMPLE 1 (2S)-2-Amino-4-ethyl-2-methylhexanoic acid

Method A

Peariman's catalyst (0.15 g) was added to a solution of(3S,5S)-3-(2-ethylbutyl)-3-methyl-5-phenylmorpholin-2-one (0.15 g, 0.54mmol, Preparation 1) in ethanol (5 ml) and 1 molar aqueous hydrochloricacid (1 ml). The reaction was stirred under hydrogen gas (414 kPa, 60psi) at room temperature for 24 hours. The reaction mixture was filteredthrough arbocel and washed with ethanol (20 ml). The liquor wasevaporated under reduced pressure and the residue was partitionedbetween dichloromethane (50 ml) and water (20 ml). The organic layer wasremoved and the aqueous phase was extracted with more dichloromethane(50 ml). The aqueous phase was evaporated under reduced pressure to givea yellow solid. The material was purified by ion exchange chromatographyon Dowex 50 WX8 resin, eluting with 0.88 aqueous ammonia:water (2:98 to14:86) to give the title compound as a white crystalline solid (30 mg).

¹HNMR (CD₃OD, 400 MHz) δ: 0.83-0.89 (m, 6H), 1.29-1.43 (m, 8H),1.58-1.62 (dd, 1H), 1.81-1.86 (dd, 1H).

LRMS (ESI): m/z 174 [M+H⁺], 172 [M−H⁻].

Method B

20 wt % Palladium hydroxide on carbon (1.0 g; 50 wt % water wet) wasadded to a suspension of4-ethyl-2-(2-hydroxy-1-phenyl-ethylamino)-2-methyl-hexanoic acid(Preparation 10, 10.0 g; 34.0 mmol) in propan-2-ol and water (4:1; 200ml). The vessel was purged three times with nitrogen then hydrogenbefore the suspension was then stirred under a hydrogen gas atmosphere(60 psi) at 80° C. for 4 hours. The resultant solution was then filteredthrough Arbocel® and washed with propan-2-ol and water (4:1; 20 ml).Propan-2-ol and water (4:1; 100 ml) was added and then distilled underreduced pressure collecting 260 ml of solvent. A further portion ofpropan-2-ol (100 ml) was added and a further 100 ml of solvent wasremoved by distillation under reduced pressure. A third portion ofpropan-2-ol (100 ml) was added and a further 40 ml of solvent removed bydistillation under reduced pressure. A viscous white slurry was thenobserved which was cooled to 22° C. The resultant slurry was stirred at22° C. for 30 minutes and the solid then isolated by filtration. Thefilter cake was washed with propan-2-ol (20 ml) and dried at 45° C.under vacuum overnight to give the title compound (3.5 g crude weight,98% purity, 20.2 mmol, 60% yield); ¹H-NMR (CD₃OD, 300 MHz), δ: 0.86 (6H,q), 1.28-1.40 (5H, m), 1.44 (3H, s), 1.57-1.63 (1H, dd), 1.80-1.87 (1H,dd).

Example 1.1 (2S)-2-Amino-4-ethyl-2-methylhexanoic acid benzene sulphonicacid salt

A solution of benzene sulphonic acid (9.5 g) in acetonitrile (50 ml) wasadded to a suspension of (2S)-2-Amino-4-ethyl-2-methylhexanoic acid (10g, 0.057 mol, Example 1) in acetonitrile (175 ml) and the mixture heateduntil dissolved. The solution was filtered whilst hot and allowed tocool overnight to give the title compound as fine white needles, (16.5g, 86%)

¹HNMR (CD3OD, 400 MHz) δ: 0.87 (m, 6H), 1.36 (m, 4H), 1.41 (m, 1H), 1.54(m, 3H), 1.75 (m, 1H), 1.88 (m, 1H), 7.42 (m, 3H), 7.83 (m, 2H), 4exchangeable not seen.

Example 1.2 (2S)-2-Amino-4-ethyl-2-methylhexanoic acidp-toluenesulphonate salt

A solution of p-toluene sulphonic acid (54 mg, 0.28 mmol) inacetonitrile (1 ml) was added to a suspension of(2S)-2-Amino-4-ethyl-2-methylhexanoic acid (50 mg, 0.28 mmol, Example 1)in acetonitrile (1 ml) and the mixture heated until dissolved. Thesolution was filtered whilst hot and allowed to cool overnight to givethe title compound as fine white needles, (69 mg, 70%)

¹HNMR (CD3OD, 400 MHz) δ: 0.88 (m, 6H), 1.36 (m, 5H), 1.54 (s, 3H), 1.75(m, 1H), 1.90 (m, 1H), 2.36 (s, 3H), 7.22 (d, 2H), 7.70 (d, 2H), 4exchangeable not seen.

Example 1.3 (2S)-2-Amino-4-ethyl-2-methylhexanoic acid hydrochloridesalt

A solution of HCl in methanol was prepared by cautiously adding acetylchloride (0.04 ml,) to methanol (1 ml). The cooled solution was added toa suspension of (2S)-2-Amino-4-ethyl-2-methylhexanoic acid (100 mg, 0.56mmol, Example 1) in methanol (1 ml) and the mixture warmed untildissolved, then evaporated under reduced pressure. The resultinghydrochloride salt was recrystallised from methanol/acetonitrile to givea white solid (63 mg, 52%)

¹HNMR (CD3OD, 400 MHz) δ: 0.87 (m, 6H), 1.36 (m, 4H), 1.43 (m, 1H), 1.55(s, 3H), 1.75 (m, 1H), 1.90 (m, 1H), 4 exchangeable not seen

EXAMPLE 2 2,5,5-Trimethyl-L-norleucine

The title compound was prepared according to the procedure outlined inExample 1 from(3S,5S)-3-(3,3-dimethylbutyl)-3-methyl-5-phenylmorpholin-2-one (0.394 g,1.43 mmol, Preparation 2). The product (0.138 g) was obtained as a whitecrystalline solid.

¹HNMR (CD₃OD, 400 MHz) δ: 0.91 (s, 9H), 1.17-1.25 (m, 1H), 1.28-1.36 (m,1H), 1.44 (s, 3H), 1.59-1.67 (m, 1H), 1.83-1.91 (m, 1H).

LRMS (ESI): m/z 174 [M+H⁺], 172 [M−H⁻].

EXAMPLE 3 (2S)-2-Amino-3-cyclopentyl-2-methylpropanoic acid

The title compound was prepared according to the procedure outlined inExample 1 from(3S,5S)-3-(cyclopentylmethyl)-3-methyl-5-phenylmorpholin-2-one (0.426 g,1.56 mmol, Preparation 3). The product (0.157 g) was obtained as a whitecrystalline solid.

¹HNMR (CD₃OD, 400 MHz) δ: 1.08-1.22 (m, 2H), 1.44 (s, 3H), 1.48-1.68 (m,4H), 1.74-2.00 (m, 5H).

LRMS (ESI): m/z 174 [M+H⁺], 172 [M−H⁻].

EXAMPLE 4 (2S)-2-Amino-5-ethyl-2-methylheptanoic acid

The title compound was prepared according to the procedure outlined inExample 1 from(3S,5S)-3-(3-ethylpentyl)-3-methyl-5-phenylmorpholin-2-one (Preparation4). The product was obtained as a white crystalline solid.

¹HNMR (CD₃OD, 400 MHz) δ: 0.85-0.92 (m, 6H), 1.16-1.48 (m, 7H), 1.56 (s,3H), 1.72-1.99 (m, 2H).

LRMS (ESI): m/z 188 [M+H⁺], 186 [M−H⁻].

EXAMPLE 5 (2S)-2-Amino-3-cyclobutyl-2-methylpropanoic acid

Pearlman's catalyst (0.5 g) was added to a solution of(3S,5S)-3-(cyclobutylmethyl)-3-methyl-5-phenylmorpholin-2-one (0.445 g,1.7 mmol, Preparation 5) in ethanol (15 ml), water (2 ml) andtrifluoroacetic acid (0.5 ml). The reaction was stirred under hydrogengas (414 kPa, 60 psi) at room temperature for 24 hours. The reactionmixture was filtered through Arbocel® and washed with ethanol (20 ml).The liquor was evaporated under reduced pressure and the residue waspartitioned between dichloromethane (50 ml) and water (50 ml). Theorganic layer was removed and the aqueous phase was extracted with moredichloromethane (50 ml). The water layer was evaporated under reducedpressure to give a yellow solid. The product was purified by ionexchange chromatography on Dowex 50 WX8 resin, eluting with 0.88 aqueousammonia:water (2:98 to 14:86) to give the title compound (0.034 g) as awhite solid.

¹HNMR (CD₃OD, 400 MHz) δ: 1.40 (s, 3H), 1.69-1.84 (m, 6H), 2.04-2.17 (m,2H), 2.41-2.54 (m, 1H).

LRMS (ESI): m/z 158 [M+H⁺], 156 [M−H⁻].

EXAMPLE 6 (2S,5R)-2-Amino-2,5-dimethylheptanoic acid

A solution of the compound of Preparation 8 (1.10 g) in dioxane (3 ml)and 6N aqueous hydrochloric acid (15 ml) was heated under reflux for 16hours. The solution was then allowed to cool to room temperature, thesolvent was evaporated and the residue was redissolved in 2 ml of water.A column of DOWEX-50X8-200 (25 g) was washed with 250 ml of deionisedwater. The crude product was then loaded and the column was eluted with250 ml of deionised water and then 250 ml of 10% aqueous ammonia. Thebasic fractions were evaporated to give the title compound (0.18 g) as awhite solid.

¹HNMR (CD₃OD, 400 MHz) δ: 0.89 (6H, m), 1.08-1.24 (2H, m), 1.26-1.49(6H, m), 1.56-1.65 (1H, m), 1.87-1.96 (1H, m).

LRMS (APCI): m/z 174 [M+H⁺].

EXAMPLE 7 (4S)-2,4-Dimethyl-L-norleucine

The title compound was prepared according to the procedure outlined inExample 1 from(3S,5S)-3-methyl-3-[(2S)-2-methylbutyl]-5-phenylmorpholin-2-one (0.586g, 2.24 mmol, Preparation 9). The product (0.018 g) was obtained as awhite crystalline solid.

¹HNMR (CD₃OD, 400 MHz) δ: 0.90-0.92 (m, 3H), 0.94-0.95 (m, 3H),1.17-1.40 (m, 2H), 1.45 (s, 3H), 1.50-1.58 (bs, 1H), 1.69-1.81 (m, 1H),1.70-1.83 (m, 1H).

LRMS (ESI): m/z 262 [M+H⁺].

The following preparations show how intermediates used in thepreparation of the Examples described above may themselves besynthesised.

Preparation 1 (3S,5S)-3-(2-Ethylbutyl)-3-methyl-5-phenylmorpholin-2-one

Boron trifluoride etherate (5.85 ml, 46 mmol) was added slowly to asolution of (5S)-3-methyl-5-phenyl-5,6-dihydro-2H-1,4-oxazin-2-one (4.35g, 23 mmol, see WO-A-02/051983) in tetrahydrofuran at −78° C. Thesolution was stirred for 50 minutes and then a solution of the Grignardreagent prepared from 3-(bromomethyl)pentane (10.9 g, 66 mmol) andmagnesium turnings (2.5 g, 99 mmol) in ether (250 ml) was added over 40minutes. The reaction mixture was stirred for a further 75 minutes at−78° C. then allowed to warm to −20° C. and quenched with saturatedaqueous ammonium chloride (100 ml). More tetrahydrofuran (100 ml) wasadded and the organic layer was separated from the aqueous layer. Theorganic layer was dried (MgSO₄) and concentrated under reduced pressure.The residue was purified by column chromatography on silica gel using anelution gradient of pentane to pentane:ether (30:70) to afford the titlecompound as a white solid (3.21 g).

¹HNMR (CDCl₃, 400 MHz) δ: 0.79 (q, 6H), 1.26-1.35 (m, 5H), 1.41 (s, 3H),1.63 (dd, 1H), 1.91 (dd, 1H), 4.17-4.26 (m, 1H), 4.28-4.35 (m, 2H),7.25-7.36 (m, 5H).

LRMS (ESI): m/z 276 [M+H⁺].

Preparation 2(3S,5S)-3-(3,3-Dimethylbutyl)-3-methyl-5-phenylmorpholin-2-one

A suspension of Rieke Magnesium (343 mg, 14.1 mmol) in tetrahydrofuran(13.7 ml) was added to a solution of 1-iodo-3,3-dimethylbutane indiethylether (50 ml) over a period of twenty minutes and the reactionwas stirred for 40 minutes at room temperature. The Grignard reagentsolution and (5S)-3-methyl-5-phenyl-5,6-dihydro-2H-1,4-oxazin-2-one (1g, 5.28 mmol, see WO-A-02/051983) were used according to the method ofPreparation 1 to generate the title compound. The total amount ofcompound synthesised was 0.394 g.

¹HNMR (CDCl₃, 400 MHz) δ: 0.91 (s, 9H), 1.13-1.31 (m, 3H), 1.42 (s, 3H),1.67-1.77 (bs, 1H), 2.02-2.10 (m, 1H), 4.31-4.43 (m, 3H), 7.34-7.46 (m,5H).

LRMS (ESI): m/z 276 [M+H⁺].

Preparation 3(3S,5S)-3-(Cyclopentylmethyl)-3-methyl-5-phenylmorpholin-2-one

The compound was prepared according to the procedure outlined inPreparation 1 using(5S)-3-methyl-5-phenyl-5,6-dihydro-2H-1,4-oxazin-2-one (1 g, 5.28 mmol,see WO-A-02/051983) and (iodomethyl)cyclopentane. The total amount ofcompound synthesised was 0.426 g.

¹HNMR (CDCl₃, 400 MHz) δ: 1.12-1.22 (m, 2H), 1.43-1.65 (m, 8H),1.78-1.94 (m, 4H), 2.13-2.18 (m, 1H), 4.23-4.42 (m, 3H), 7.31-7.45 (m,5H).

LRMS (ESI): m/z 274 [M+H⁺].

Preparation 4 (3S,5S)-3-(3-Ethylpentyl)-3-methyl-5-phenylmorpholin-2-one

The title compound was prepared from(5S)-3-methyl-5-phenyl-5,6-dihydro-2H-1,4-oxazin-2-one (0.454 g, 2.39mmol, see WO-A-02/051983) and 1-bromo-3-ethylpentane (see Bull. Soc.Chim. Fr., 1975, 201-205) according to the procedure outlined inPreparation 1. The total amount of compound synthesised was 0.07 g.

¹HNMR (CDCl₃, 400 MHz) δ: 0.91 (s, 9H), 1.13-1.31 (m, 3H), 1.42 (s, 3H),1.67-1.77 (bs, 1H), 2.02-2.10 (m, 1H), 4.31-4.43 (m, 3H), 7.34-7.46 (m,5H).

LRMS (ESI): m/z 276 [M+H⁺].

Preparation 5(3S,5S)-3-(Cyclobutylmethyl)-3-methyl-5-phenylmorpholin-2-one

The title compound was prepared from(5S)-3-methyl-5-phenyl-5,6-dihydro-2H-1,4-oxazin-2-one (1 g, 5.28 mmol,see WO-A-02/051983) and (bromomethyl)cyclobutane according to theprocedure outlined in Preparation 1. The total amount of compoundsynthesised was 0.445 g.

¹HNMR (CDCl₃, 400 MHz) δ: 1.43 (s, 3H), 1.73-1.82 (m, 2H), 1.86-1.92 (m,2H), 2.02-2.12 (m, 2H), 2.14-2.19 (m, 1H), 2.43-2.52 (m, 1H), 4.22-4.27(m, 1H), 4.33-4.37 (m, 2H), 7.31-7.43 (m, 5H).

LRMS (ESI): m/z 260 [M+H⁺].

Preparation 6 (5R)-5-Methylheptan-2-one

Dicyclohexyl carbodiimide (9.51 g, 46.1 mmol),N,N′-dimethyl-4-aminopyridine (1.13 g, 9.2 mmol) and triethylamine (6.4ml, 46.1 mmol) were added to a solution of Meldrum's acid (6.64 g, 46.1mmol) in dichloromethane (150 ml). (4R)-4-Methylhexanoic acid (6 g, 46.1mmol) was added and the reaction mixture was stirred overnight. Thereaction mixture was filtered and the solid was washed withdichloromethane (2×100 ml). The filtrate and washings were combined andevaporated under reduced pressure to give an orange oil. Acetic acid (50ml) and water (50 ml) were added and the reaction was heated underreflux overnight. After the solution had cooled to room temperature itwas extracted with pentane (100 ml). The organic extract was dried(MgSO₄) and evaporated to give a residue that was purified by columnchromatography on silica gel using an elution gradient of pentane topentane:diethyl ether 19:1 to give the title compound (2.8 g) as a paleyellow oil.

¹HNMR (CDCl₃, 400 MHz) δ: 0.82-0.88 (6H, m), 1.07-1.19 (1H, m),1.25-1.41 (3H, m), 1.54-1.64 (1H, m), 2.12 (3H, s), 2.34-2.47 (2H, m).

Preparation 7N-[(1E,4R)-1,4-dimethylhexylidene]-(S)-2-methylpropane-2-sulfinamide

A solution of (5R)-5-methylheptan-2-one (3 g, 23.4 mmol) intetrahydrofuran (10 ml) was added to a solution of(S)-2-methylpropane-2-sulfinamide and titanium tetraethoxide (9.8 ml,46.8 mmol) in tetrahydrofuran. The solution was stirred at 50° C. for 20hours. The reaction mixture was allowed to cool to room temperature,diluted with ethyl acetate (50 ml) and then poured into brine (100 ml).

The layers were stirred vigorously for 2 minutes and then filtered. Theorganic layer was separated from the aqueous layer and dried (MgSO₄).The solvent was evaporated under reduced pressure and the residue waspurified by column chromatography on silica gel using an elutiongradient of 1:9 ethyl acetate:pentane then 3:17 ethyl acetate:pentane.This gave the title compound as a pale yellow oil (3.6 g).

¹HNMR (CDCl₃, 400 MHz) δ: 0.82-0.91 (6H, m), 1.10-1.23 (10H, m),1.29-1.43 (3H, m), 1.54-1.65 (1H, m), 2.15 (0.6H, s), 2.30 (2.4H, s),2.32-2.72 (2H, m).

LRMS: m/z ESI 232 [M+H⁺].

Preparation 8N-[(1S,4R)-1-cyano-1,4-dimethylhexyl]-2-methylpropane-(S)-2-sulfinamide

Isopropanol (0.63 ml, 8.2 mmol) was added to a mixture of a 1 molarsolution of diethylaluminium cyanide in toluene (12.3 ml) andtetrahydrofuran (5 ml). The mixture was stirred at room temperature for10 min and then cooled to −78° C. A solution of the compound ofPreparation 7 (1.9 g, 8.2 mmol) in tetrahydrofuran (20 ml) was addeddropwise over 2 minutes. The reaction was then stirred at −78° C. for 5minutes and at room temperature for 90 minutes. The reaction mixture wasthen cooled to −20° C. and poured onto a vigorously stirred mixture ofethyl acetate (100 ml) and water (100 ml). The mixture was filteredthrough Arbocel® and the ethyl acetate layer was separated and dried(MgSO₄). The solvent was evaporated under reduced pressure and theresidue was purified by column chromatography on silica gel using anelution gradient of 1:4 ethyl acetate:pentane then 3:7 ethylacetate:pentane. This gave the title compound as a white solid (1.10 g).

¹HNMR (CDCl₃, 400 MHz) δ: 0.86-0.93 (6H, m), 1.13-1.26 (10H, m),1.29-1.44 (3H, m), 1.48-1.57 (2H, m), 1.64 (3H, s), 1.81-1.98 (2H, m),3.41 (1H, s).

LRMS (APCI): m/z 259 [M+H⁺].

Preparation 9(3S,5S)-3-Methyl-3-[(2S)-2-methylbutyl]-5-phenylmorpholin-2-one

The title compound was prepared from(5S)-3-methyl-5-phenyl-5,6-dihydro-2H-1,4-oxazin-2-one (1 g, 5.28 mmol,see WO-A-02/051983) and (2S)-1-iodo-2-methylbutane according to theprocedure outlined in Preparation 1. The total amount of compoundsynthesised was 0.586 g.

¹HNMR (CDCl₃, 400 MHz) δ: 0.85-0.88 (m, 3H), 0.94-0.96 (m, 3H),1.17-1.40 (m, 3H), 1.46 (s, 3H), 1.60 (bs, 1H), 1.73-1.78 (m, 1H),1.88-1.93 (m, 1H), 4.22-4.42 (m, 3H), 7.28-7.42 (m, 5H).

LRMS (ESI): m/z [M+H⁺].

Preparation 104-Ethyl-2-(2-hydroxy-1-phenyl-ethylamino)-2-methyl-hexanoic acid

To a solution of (5S)-3-methyl-5-phenyl-5,6-dihydro-2H-[1,4]oxazin-2-one(5 g, 26.4 mmol, see WO-A-02/051983) in anhydrous2-methyltetrahydrofuran (50 ml) was added boron trifluoridetetrahydrofuran complex (5.8 ml, 52.8 mmol) with stirring under nitrogenat −78° C. The resultant solution was then stirred at −78° C. for 1hour. (2-Ethylbutyl)magnesium bromide as a solution in tetrahydrofuran(170 ml, 0.16 M, 27.7 mmol) was then added maintaining the temperaturebelow −60° C. during the addition. The resultant solution was stirred at−78° C. for a further 2 hours. Acetic acid (0.6 ml 10.6 mmol) was thenadded and the solution warmed to 22° C. Saturated aqueous ammoniumchloride (50 ml) was then added followed by water (100 ml). The phaseswere separated and the organic phase retained. The resultant solutionwas then distilled to dryness under vacuum. Toluene (75 ml) was thenadded and the organic solution was washed with water (25 ml) thensaturated aqueous sodium chloride solution (25 ml) and the phasesseparated and the organic phase retained. Aqueous hydrochloric acid (100ml, 1.5 M) was then added and the resultant biphasic mixture warmed to30° C. and stirred for 2 hours. The phases were separated and theaqueous phase retained. Aqueous sodium hydroxide (47% w/w, 6 ml then 2M,16 ml) was then added to give a pH of 5 by pH paper. The resultantslurry was stirred at 22° C. for 30 minutes and the solid was thenisolated by filtration. The filter cake was washed with water (25 ml)and dried at 60° C. overnight under vacuum to give the title compound(4.1 g crude weight, 95% purity, 14.0 mmol, 53% yield): mp 149° C.;¹H-NMR (CD₃OD, 300 MHz), δ: 0.83 (3H, t), 0.90 (3H, t), 1.06 (3H, s),1.31-1.54 (5H, m) 1.73 (2H, d), 4.40 (1H, t), 7.46-7.50 (5H, m); LRMS(ES): m/z 293 [M]⁺.

1. (2S)-2-Amino-4-ethyl-2-methylhexanoic acid or a pharmaceutically acceptable salt thereof.
 2. A compound of claim 1 wherein the compound is (2S)-2-amino-4-ethyl-2-methylhexanoic acid.
 3. A compound of claim 1 wherein the compound is a pharmaceutically acceptable salt of (2S)-2-amino-4-ethyl-2-methylhexanoic acid.
 4. A compound of claim 3 wherein the compound is a benzene sulphonic salt of (2S)-2-amino-4-ethyl-2-methylhexanoic acid.
 5. A compound of claim 3 wherein the compound is a p-toluenesulphonate salt of (2S)-2-amino-4-ethyl-2-methylhexanoic acid.
 6. A compound of claim 3 wherein the compound is a hydrochloride salt of (2S)-2-amino-4-ethyl-2-methylhexanoic acid.
 7. A pharmaceutical composition comprising (2S)-2-amino-4-ethyl-2-methylhexanoic acid, or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable excipient.
 8. A pharmaceutical composition of claim 7 wherein the composition comprises (2S)-2-amino-4-ethyl-2-methylhexanoic acid.
 9. A pharmaceutical composition of claim 7 wherein the composition comprises a pharmaceutically acceptable salt of (2S)-2-amino-4-ethyl-2-methylhexanoic acid. 